[molson]

It's a crime to incite violence or disturb the peace now even if you don't burn a flag along with it. The act of burning a flag for protest doesn't convert those criminal activities into constitutionally protected ones. Though burning the flag couldn't itself be the only evidence of the intent to do one of those things.

Edit: And it's REALLY hard to prove intent to actually incite violence - calling for violence in the abstract is not enough (which is why Trump couldn't be prosecuted for some of his campaign bluster). So there really wasn't anything to that Flag Protection Act, it didn't make illegal any new activity, it was just for show. But it was still kind of symbolically hostile to that form of protesting, so I can see why people would oppose it.