So it’s immoral to force your will on a cat regarding their diet when they themselves would choose different is immoral but forcing your will on cows/pigs by killing them even though they would choose to live is not?

Cats, like humans, need certain nutrients (macro and micro), they don’t need that nutrients from a specific source. Of course a healthy vegan diet needs effort and monitoring to ensure sufficient intake of these nutrients, but it’s certainly possible, both for humans and cats.