How exactly is honoring Mary distracting us from Jesus?

Regarding how Protestants generally view Catholic adoration of Mary, the following is fairly representative of most Protestant suspicions. First, your question as to how honouring Mary could distract from honouring Christ. In view of what Jesus said himself about due honour, his words show why giving undue honour dishonours both Christ and God:

"For the Father judgeth no man, but hath committed all judgment unto the Son: that all men should honour the Son even as they honour the Father. He that honoureth not the Son honoureth not the Father which hath sent him." John 5:22-23 A.V.

"And ye will not come to me, that ye might have life." John 5:40

Him that cometh to me I will in no wise cast out... No man can come to me, except the Father which hath sent me draw him." John 6:37 & 44

This shows only one way of approach to God - via the risen Son and the Father. Mary is never mentioned in scripture as a means of approach. And Jesus assures us that if we go directly to and through him, we will never be cast aside, so there is no basis for Catholic ideas about the Father being more sympathetic to Mary's pleadings on our behalf than Jesus'. Jesus is our great High Priest, and the only Mediator between God and men - Hebrews 7:24-26 & 8:6 & 9:11; 24-28. It would be giving Mary undue honour to equate her with Jesus' unique role in heaven as our great High Priest, and our only Mediator. If another mediator, in addition to Christ, was needed, then Christ would then be an incomplete, insufficient Mediator. That would dishonour Christ.

Mary is certainly to be greatly respected for she was declared to have found favour with God, and blessed among women (Luke 1:28-30). She certainly knew things about Jesus that she treasured in her heart, but the scriptures do not indicate that she was brought into apostleship or given any role in the new church after the resurrection. She has always remained exemplary, especially to Christian women, but to elevate her the way Catholics and Orthodox do is alarming, especially regarding praying to Mary.

Catholics pray to Mary and prayer is a vital form of worship. However, because Catholicism knows it's on a sticky wicket there, it has worded its way out of the charge of worship (so it thinks). Rome teaches (1) that the virgin Mary and other saints and angels are to be given a degree or kind of religious worship. (2) they are to be invoked for help in time of need; (3) they are able to intercede with God or with Christ for us; (4) God may be asked to save and help us, at least in part, on the ground of the merits of the saints; (5) the pictures, images, and relics of saints and martyrs are to be retained in churches and worshipped - see the decrees of the Council of Trent.

"To avoid the charge of idolatry... they distinguish between (a) Latria, or the highest religious worship which is due to God alone and (b) Doulia - inferior religious worship due in various degrees to saints and angels according to their rank. They also distinguish between (c) direct worship due to God, to the Virgin or to the saints and angels, and (d) indirect worship which terminates upon the picture or image which represents to the worshipper the direct object of his worship" - The Confession of Faith, p 273.

Protestants protest that the scriptures clearly forbid any kind of worship of men or angels - see Acts 14:14,15, Col. 2:18; Acts 10:25-26 Rev. 19:9-10 & 22:8-9. But because Catholicism puts papal decrees higher than the scriptures, they try to wriggle out of this with semantic arguments. As for praying, Jesus gave permission to His followers to pray to Him after He'd returned to Heaven, but no human being is to be prayed to. He alone is our great High Priest and our Mediator. The Holy Spirit is the one who takes our prayers to God and presents them before God and Christ in Heaven and mediates for us. See Romans 8:26-27 & Hebrews7:25.

Stick to the scriptures, and only God is worshipped, with Christian prayer being worship. No human even comes close to such adoration. And angels forbade humans to fall down before them. Not Christ, however, for he is God.

Mary's Catholic titles of "Queen of Heaven" and "Mother of God" have already been dealt with at length on this site. I gave an answer on whether the early Church Fathers believed Mary to be 'Queen of Heaven' at Did the Early Church Fathers believe that Mary was the queen of heaven?

'Theotokos' (God-bearer) was applied to Mary at Chalcedon, 451, but only as to the manhood of Christ, not his deity. Clergy, like Nestorius, objected to the Catholic populace misunderstanding this and venerating Mary as the supposed "Mother of God". He said that the Bible never says that God was born of the Virgin. It only speaks of the incarnation of the Logos, not of his birth. He added that although others like Origen and Athanasius had used the term theotokos, it had not been incorporated into either the Nicene (321) nor the Constantinopolitan (381) creeds.

For starters, it smacks of idolatry.

While there is certainly nothing wrong with loving our fellow humans (indeed, that is the second of the new commandments!), we are to love God (Jesus) first. The Catholic "obsession" with Mary (and, to an extent, other saints) might seem, especially to an outsider, to infringe upon this priority.

Indeed, appearance is another important aspect. When a Catholic seems to be honoring Mary before God, whether that's truly the case or not, that appearance gives the wrong message to non-believers, non-Catholic believers, and potentially even other Catholics. Christians are admonished several times in the epistles to be wary of anything that may cause a brother to doubt, especially things that are not needful... and reverencing Mary is not needful.

Mary is not our Savior. Only Jesus Christ is our savior. Thus, another answer is shown already in the title of your question; it's a distraction. Now, if a little Marianism truly brings you closer to Christ... well and good. But if one continues to devote their attention to a (dead) human rather than to God, that attention is ultimately misplaced, and one ought to repent.

Mary is also not our intercessor. Praying to Mary (or to saints), rather than to God, is deliberately distancing one's self from the God one claims to love. Why would someone who loves God ever want to pray to someone else, rather than to God directly?

Although the argument is often made that we ask other, living humans to pray for us... that is clearly a different case. First, if we're doing so primarily, rather than as a supplement to praying to God directly, it's clear that we're doing something wrong. Second, asking for prayer from a living person encourages fellowship and fulfills a secondary function that God has commanded of Christians "looking out" for each other and sharing their burdens. It works to our benefit in a way that talking to people no longer living in this world can't and won't. This is an important point; the purpose of asking others to pray for you is not to "gang up" on God, it's to share your burdens with those who can help. God can help, because... well, because He's God. Living people can help because we interact with them in this life. Those who have fallen asleep have no physical presence (and many Christians believe they have no ability at all to influence the present, physical world) nor do they have God's omniscience.

Another point... why care about Mary, and not about Joseph? If you've never given Joseph a second thought... you might want to think long and hard about why. You may say "no one knows Jesus like Mary", but surely Joseph is a close second? If you aren't giving Joseph at least half as much attention as you're giving Mary, if you aren't giving the apostles (who were with Jesus continually during His ministry), you probably need to seriously look at why you're holding Mary in such reverence. Yes, she was chosen by God to fulfill a very special purpose, but so was Abraham. So were Moses and Noah.

Claiming that Mary is "alive" is irrelevant. If our criteria for reverence is those who have (eternal) life in Christ, then Mary is no more worthy of our devotion than Abraham, Moses, David, Matthew, Mark, Peter, Paul, the one thief crucified beside Christ, or your Christian grandfather.

What of the claim that Mary is the "queen of heaven"? What of it? "Thou shalt have no other gods before me," declares the LORD (Exodus 20:3). At best, we are still commanded, clearly, to put God first. Moreover, the scriptural basis for this claim is questionable, and many Protestants reject it. Where scripture does mention a "queen of heaven", God has this to say about the dwelling of those who worship her: "Behold, my anger and my wrath will be poured out on this place, upon man and beast, upon the trees of the field and the fruit of the ground; it will burn and not be quenched." (Jeremiah 7:20)

That said, it's no more sinful to respect or study Mary than to respect or study Sir Isaac Newton, or Saint Augustine, or Saint Paul, or one's parents (Exodus 20:12). But we ought not pray to any of these people. We ought not let our respect or study get in the way of worshiping God or studying His Word, lest we find ourselves putting them before God. And we ought to be careful about giving the appearance of doing so, lest we cause others to stumble.