There is no one rule to fit all vegans, every vegan has to evaluate their own situations. You are right that some vegans are against all pet ownership. There is another group that believes if you rescue an animal from being euthanized or slaughtered and improve their standard of living and length of life, then that is ethical.
A huge part of being vegan is repetitive self-reflection, always searching for moral inconsistencies and working to fix them.
This is what leads vegans to consider a vegan diet for their pet, as if it was at least as healthy as non-vegan food, then less animals will be hurt due to the vegans choices.
Contrary to popular belief there are plenty of studies and case reports advocating for both sides of the argument of vegan cat food. Even by the admins new rules, we would be able to argue for vegan cat food as long as we only referenced studies.
Since its not settled either way, and multiple pet health and food organizations have stated their interest in researching the viability of vegan/vegetarian diets for dogs/cats, I think its fair to say it should be open for discussion.
If its just a you-and-them conversation why are you making appeals to popular opinion?
Do you believe having the popular opinion means its the right one?