The Constitution says that ANY political speech, is protected speech, even if it is lying, and even if the vast majority are against it.
Flying the ISIS flag, might prove you are a dumba**, but you do have the right to make a political statement with it, if you choose to.
I think American Nazi Party leader George Lincoln Rockwell used to fly a Nazi flag over his compound.
He actually named his compound ‘Hatemonger Hill’ and it was at the end of the street that one of my friends lived on when I was in middle school. We had a carful of wannabe Nazis stop and ask us for directions one time. They weren’t exactly an impressive bunch.