Yes, they can, when used very selectively and very carefully, in very specific ways, which they rarely are
Boycotts can work, but you should be very careful and selective in using them -- you should think very carefully about who will be impacted by your boycott, and how. Specifically, if you are trying to work to decrease the suffering of the victims of some policy (what activism is supposed to be all about), then your boycott should actually work that way -- it should, at a minimum, not make those victims suffer more -- and it should also not distract attention away from their plight/suffering.