Reasons against practicing insight meditation as a main (sitting) practice for medical or other recondite-subject majoring students?

There are 4 ways your meditation develops

(1) insight preceded by calm 
(2) calm preceded by insight
(3) calm coupled with insight
(4) a mind seized by restlessness

(Yuga,naddha) Paṭipadā Sutta

If you take (1) - (3) calm and insight are both present but only different in order in which they are developed. Hence both are needed, through the order they develop will differ.

Also see: Samatha and Vipassanā, The Buddha Discovered Dhyana

Insight meditation doesn't cause defilements.

Insight meditation causes one to be able to see the defilements that have always been there.

 Real education consists in drawing the best out of yourself. -Mahatma Gandhi

Have you tried the instructions from this booklet? Seems very basic and simple, but it's actually not easy to do and quite profound. I wouldn't intellectualize about it too much (like reading studies or books). Bhikkhu Bodhi used the analogy that this is like going into a restaurant, reading the menu and then leave without eating anything.

I'm linking this talk by Ajahn Sumedo which I personally found very helpful. I don't find the source, but there is a Buddha quote that goes like 'sati (mindfulness) is always useful'. So if you find time to even meditate on your breath that's great. Also just reminding in what posture you're in (sitting, walking, lying, standing) I find to be a very powerful tool.

I've never heard the term mindfulness-based, but in general mindfulness (= reminding, reaffirming what's present) is the practice and insight (= clear understanding, knowing) is the result (likewise if you clean your house cleaning is the practice, the clean house is the result).

I did my first longer vipassana retreat while I was a postdoc researcher (applied math and numerics), and did many more since then. I found it beneficial to have days/weeks dedicated for intense practice (which are tough, but you're in a protected environment) and then off-retreat time for work & other stuff. After retreats, I was mostly much more creative in work (especially after the first one; I finished within weeks papers I had been writing for months), as retreats remove a lot of negative conditions which we carry around. Sometime there were difficult post-retreat states, true, but you want to learn to face those as well.

I would not be afraid that light (1 hours and such) daily practice will cause some substantial trouble in your life; it's more about seeing stuff which is happening anyway. If you have a competent teacher, he can help you to adjust your practice if you think there is some difficulty.

That said: if you have some serious psychological condition, don't forget to take care of it along the way, using also conventional means (psychotherapy, medication) as necessary. Traditional 3 Buddhist trainings are (1) personality (they call it "morality", but it is really about having a stable psycho-social basis, as I understand it) (2) concentration (3) insight; and the first one has to be strong enough to support the other ones.

Vipassana (=3) as such does not imply separate concentration training (=2). Some schools do that (e.g. Goenka which you seem to mention implicitly -- anapanasati, then bodyscanning) but the "dry vipassana" approaches (Mahasi and similar) don't; you do vipassana and build up concentration along the way.

Being a dry person, I personally do the dry vipassana. It is very important to include all 4 foundations of mindfulness (body, feeling, mind, mind objects) in the practice. High concentration is not necessarily good; I was depressive for years and had terrible (though successful) life as a result of being very concentrated and pushing stuff away without even knowing that. In fact if you are doing PhD, odds are that your concentration is rather high. You maybe hope that if you concentrate more, you will be more successful; maybe, but maybe you won't be very happy, and maybe you will run into burn-out. It is important to be flexible with concentration (to be able to release it), to not become its slave. Concentration sometimes causes people to be excessively serious.

PS (added): "Mindfulness-based" is sometimes used to refer to secular contemplative approaches often based on vipassana, such as MBSR (mindfulness-based stress reduction), MBCT (mindfulness-based cognitive therapy) etc. You will find both mindfulness/insight meditation used as translations of vipassana (meaning "seeing distinctly/clearly"); I personally find "insight" more appropriate, since insight is the goal and mindfulness (sati) only the means, though mindfulness might become prevalent, sounding perhaps less mysterious...