There lies a very big difference between a revolutionist and an extremist.
Revolutionaries are the people who want to bring about a change.They protest against something which is not correct and make attempts to change it.They do it in a manner considered to be polite and need not involve violence though the history has witnessed a lot of bloodshed whenever a revolution began.But the main idea behind a revolution is to correct something which is incorrect.Something which can be turned into something better.
However,an extremist follows the policy of "Give me what I want,or I'll snatch it anyway." He doesn't care if just for hi naive demands,a hundred people he kills of gets killed or a thousand.He just believe what he's doing is the only right thing to do and so he goes to extreme measures and extreme limits to fulfill his whims and fancies.Need I remind you that there's no good cause for what he kills people or creates chaos?
A revolutionist aims at changing today so that tomorrow can be beautiful for the upcoming generations, but an extremist aims at fulfilling his desires at the cost of others lives.