Like do they actually, reliably effect change in the way the activists intend?

Have they worked against Israel? Did they work against Apartheid South Africa? Could they work against Trump’s America?

My hunch is that they don’t, really, but can be a useful promotional tool for other issues. Like don’t buy American is a simple message. >If people will listen to that, they may listen to reasons why, which maybe could build a movement.

But on the whole I am very sceptical, and would be interested in any reasons for or against boycotts.

Try to look at it the other way around: Every single one of your actions is a vote for how you want the word to be. By the very act of visiting a country you declare that country to be worth visiting, by purchasing a product you endorse it, by using a service you support the continued existence of that service and all things connected to it.

Now why wouldn’t the reverse be true?