The effectiveness of it depends entirely on your plan. I don't really condone it, but obviously destroying stuff does destroy the value of things. Going around blowing stuff up is a type of warfare. While protests are a way to change things they are not warfare, so you can't really compare the two. Violence at a protest and rioting isn't expression or warfare, it is just random chaos and random chaos doesn't really produce positive results.

If you are going to go to war with someone, you don't do it as a mob with random destruction and chaos.