Depends on the protest.
Shouting out a speaker isn't stopping them speaking, it's stopping them being heard (there's a huge difference here, though it's one I expect that Mr Nuance himself can't see).
There's also protest to express disagreement / dissatisfaction, rather than prevention (eg the anti-Brexit marches), and protests who's longer term aim may be the prevention, but no expectation that the individual protest itself is going to make a huge difference (eg anti-war protests, climate change, or simple strikes)