[AFAIK]

I see a lot of defeatism about boycotts expressed on social media. The idea being that if you still buy somethings sometimes then the company that's just seen it's revenues drop 15% will ignore you. Let's say you convince half of McDonalds' customers to eat somewhere else half the time. That means 50% of customers have reduced their consumption by 50%, which adds up to a 25% drop in revenue. That's going to get the attention of any board of directors.

If and when you pressure McD's to change its policies you can move on to boycotting Burger King, then KFC and so on until you've successfully changed the industry standard. This tactic has been used successfully many times. Most recently by moving chickens out of cages and into barns where they have more space and more freedom of movement.