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.
Know what works better than boycotts? A general strike. Stop the economy in its tracks. Have a clear, articulated goal. No leadership. No one to arrest. No one to identify as a troublemaker.
The trouble, when systemic, is the system. A boycott is meant to strike at an individual or group of allied organization(s). A general strike is the last level.
Governments tend to be allergic to general strikes. Their reactions are heavy-handed, thoughtless, and reactionary. Howard Zinn recounts several in A People’s History of the United States. But, when primed and done well, it is a demonstration of political will unlike any other. It is a change agent.
I was in Guatemala in 2015 for the one-day general strike that led to the arrest of then-President Otto Perez Molina. His party had been funnelling tax revenues into a slush fund. Look up #noletoca and #LaLinea. He was removed from the presidency, tried, convicted, and served time.