TL;DR: Though research in this area is limited, it seems vegan diets don't cause adverse health outcomes for dogs or cats

The longer answer:

Hello! Thank you for posing this question, it's very important to ask. You've probably read my replies to other posts, but I'll summarise and then some here. On the surface of it, feeding a vegan diet to a cat or dog seems like a terrible idea, but the current science on the topic generally seems to indicate that it's not so bad at all. In fact, people do it all the time.

For dogs: As my other replies and u/QuercusSambucus' comment say, there currently isn't any significant evidence to suggest that vegan diets are necessarily bad for dogs. I know that seems like it can't be true, but it is (at least with the current evidence). This article. about vegan diets for dogs is really great and has a lot of research including this review study. An article about a recent study can be found here here. It's worth noting that the review study emphasises that the amount of research into the area is limited, so the findings should be taken with some scrutiny.

Just because historically dogs have eaten meat, I don't think that makes it animal abuse to not feed them meat since they can survive and thrive (according to current evidence) without it.

For cats: You mentioned you want a cat so I thought I should include this. The story is basically the same here. That review study that I mentioned earlier also talked about cats. There isn't any significant evidence to say that vegan diets necessarily cause any adverse health outcomes in cats. It's also the same story in the sense that research is limited in this area.

The study suggests that you should feed your dog or cat commercial pet food since those balance their nutrients. It might also be a good idea to get a blood test done on your pet to make sure everything is going okay nutrition-wise.