Being vegetarian or vegan IS a choice
For some people is a choice in the same way that being kosher or halal is a choice, it's religious or cultural.
For others (like me) yes, it's a choice, but it's a choice between being able to do my job effectively (I'm a therapist, dealing with clients one on one) or having to run to the toilet regularly and having to allow extra time between clients so I can go over time if I need to.
By choosing vegan options at a place that sells meat doesn't support the slaughter of animals. That's just a ridiculous emotive argument. Do you think that, if everyone started buying the vegetarian and vegan options instead of the meat ones, they would keep the slaughterhouses going? Hardly. (yes, I know that's not going to happen).
More and more places are offering vegan options. So clearly it is something they see as worth investing in, and is making them money. They wouldn't offer it otherwise. And yes, that includes places that sell chicken and burgers. In fact some have paid for very expensive marketing campaigns to get the message out about their new products.