I have NEVER protested, complained or boycotted a restaurant for menu items (vegetarian, GF, etc.). Political messages, yes. But not about food.
Maybe I should. Vegans et al can ‘request’ their food prepared a certain way, no different than I request food be prepared in butter, etc.
I shouldn’t be compelled to read emotional/political statements in a menu.
Some foods are like that. For example, you cannot prepare Kosher foods with the same pots/pans/plates as non-Kosher food.
I guess you can invoke the mantra of “The Customer is Always Right”. The problem here is that the owners catered to a customer base that was fundamentally activist. I guess it worked for a while, but nothing lasts forever. I read once that very few restaurants last more than 3 years. And the reason is not just customers; you also have to survive the insane dictates of the local Department of Health. Had a neighbor who ran a popular Chinese restaurant and the local DOH drove him out of business. He could not get a 3rd mortgage on his house to meet their mandatory modifications they suddenly wanted for his restaurant.