I think “the money is made from animal parts and there are no fully vegan cars so you’re arbitrarily picking and choosing when to be vegan” misses the point of ideological veganism. I’m not a vegan, but I believe the goal for ideological vegans (in contrast with those who are vegan for medical reasons) is to minimize suffering and exploitation within reason for the specific reasons you said. No one can be 100% free of animal parts unless they become an off-the-grid self-sustained homestead.

Vegans know that. But most come to the conclusion that just because you can’t live 100% animal free doesn’t mean you can’t try to get to 80% because you want to live your life in a manner you consider morally and ethically consistent with your collective ideologies. You get as close as you can within reason depending on the various constraints of your individual circumstances. “I am still a vegetarian, and I try to be a vegan, but I occasionally cheat. If there’s a cheese pizza on the band bus, I might sneak a piece,” to quote Weird Al Yankovic.

I’d say most people, including vegans, have more than one goal in life. The “lines in the sand” you’re referring to are at the intersection of their goal to minimize suffering and their goal to, say, keep living. Like if a vegan were told by their doctor, “If you don’t start eating meat, you’ll die from this weird disease,” the vegan likely wouldn’t be like, “Well, I might as well indulge in eggs and milk and all other animal products now since I can’t be 100% vegan” and chow down. They’d probably eat just the amount prescribed by their doctor, because they still don’t like eating meat because its origins bother them.