Did the Latins see the Etruscans as a plague?

The Etruscan civilization is certainly enigmatic, but they did have - like all other civilizations of the era - a persistent military tradition, which included a series of major conflicts with the Romans. A lot of military or military related concepts & practices that are today commonly associated with the Romans are actually Etruscan borrowings. A notable example is the Triumph, at least according to Strabo (Geography 5.2.2):

The Tyrrheni have now received from the Romans the surname of Etrusci and Tusci. The Greeks thus named them from Tyrrhenus the son of Atys, as they say, who sent hither a colony from Lydia. Atys, who was one of the descendants of Hercules and Omphale, and had two sons, in a time of famine and scarcity determined by lot that Lydus should remain in the country, but that Tyrrhenus, with the greater part of the people, should depart. Arriving here, he named the country after himself, Tyrrhenia, and founded twelve cities, having appointed as their governor Tarcon, from whom the city of Tarquinia [received its name], and who, on account of the sagacity which he had displayed from childhood, was feigned to have been born with hoary hair. Placed originally under one authority, they became flourishing; but it seems that in after-times, their confederation being broken up and each city separated, they yielded to the violence of the neighbouring tribes. Otherwise they would never have abandoned a fertile country for a life of piracy on the sea. roving from one ocean to another; since, when united they were able not only to repel those who assailed them, but to act on the offensive, and undertake long campaigns. After the foundation of Rome, Demaratus arrived here, bringing with him people from Corinth. He was received at Tarquinia, where he had a son, named Lucumo, by a woman of that country. Lucumo becoming the friend of Ancus Mar- cius, king of the Romans, succeeded him on the throne, and assumed the name of Lucius Tarquinius Priscus. Both he and his father did much for the embellishment of Tyrrhenia, the one by means of the numerous artists who had followed him from their native country; the other having the resources of Rome. It is said that the triumphal costume of the consuls, as well as that of the other magistrates, was introduced from the Tarquinii, with the fasces, axes, trumpets, sacrifices, divination, and music employed by the Romans in their public ceremonies. His son, the second Tarquin, named Su- perbus, who was driven from his throne, was the last king [of Rome]. Porsena, king of Clusium, a city of Tyrrhenia, endeavoured to replace him on the throne by force of arms, but not being able he made peace with the Romans, and departed in a friendly way, with honour and loaded with gifts.

That said, most of what we know about the Etruscans comes from Livy (59 BC – AD 17), and apparently he was more interested in glorifying his own people (and vilifying their enemies, including the Etruscans), than getting his facts straight. One of his (many) known errors was the claim that the Etruscans hailed from Northern Europe, a claim that contradicted the (much earlier) view of Herodotus that they were of Aegean / Anatolian origin. Herodotus' side of the story was verified (more or less) in 2007 when a study showed that mitochondrial DNA Variation of modern Tuscans supported the near eastern origin theory.

I can't find a specific reference that the Latins considered the Etruscans "a plague". However, describing the Etruscans as "peaceful merchants" is not exactly accurate either. Given that they often clashed with the Romans and that Livy's works were widely circulated at the time, it's not unreasonable to suggest that - at least for a time - the Romans viewed the Etruscans unfavourably. They were, after all, conquered, and history is usually written by the victors.

Further reading:

• A Brief History by the Victor: Roman Portrayal of Etruscan Influence, by MaryLee Franks
• Societies, Networks, and Transitions: A Global History, by Craig A. Lockard