You're parroting meat industry talking points. PETA's behaviour clearly indicates this is not the case, as they help substantially more animals than they euthanize. In a given year the vast majority of their interactions are spaying/neutering, providing other free or low cost medical services, and helping unhoused backyard dogs.

They even adopt some of these animals themselves. Why would they adopt them if they were ideologically opposed to adoption. Simple answer: they aren't.

They're likely ideologically opposed to the concept of animals as property, as opposed to companions, which is why they use terminology like "guardian/companion" instead of "owner/pet".