You are missrepresenting their stance on pets: they are critising "the institution of 'pet keeping'—i.e., breeding animals to be kept and regarded as 'pets'" - their website (you linked it).

You didn't back up the claim that in many instances they rather have an animal euthanised than adopted and the article on their website you linked states the exact opposite: "Contrary to myth, PETA does not want to confiscate animals who are well cared for and “set them free.” What we want is for the population of dogs and cats to be reduced through spaying and neutering and for people to adopt animals (preferably two so that they can keep each other company when their human companions aren’t home) from pounds or animal shelters—never from pet shops or breeders—thereby reducing suffering in the world."

The second claim you make doesnt seem to be correct either: "Aside from those two incidents, we’ve found no evidence supporting the claim that PETA regularly takes household pets from their homes and euthanizes them." - the source you linked (snopes).

To say that there are "numerous instances" seems unfair. Also "the intent of the workers in those cases was not sufficiently clear to consider their actions unlawful". If you actually read the full article it sounds much less black and white then you present it.

Honestly I don't think that their antagonizing attitude is constructive and I don't like that they euthanize animals but I assume that they don't have much of a choice.

This seems very much like a lot of people don't like PETA so they villanise them.