It's not BS it's reality. Especially for older generations, but not only, the way other people perceive them and their beliefs is important. If by supporting vegetarianism, climate advocacy, et. al they will be perceived as supporting these types of actions they won't do it. Is it stupid? Absolutely, but it's reality and a demographic of people you won't be getting for your cause and for climate we can't afford to lose credibility and supporters.
With this lack of nuance and understanding is how the left loses voters to the far right, and how activists lose supporters they can't afford to lose