When it comes to speech, it can't be free when you like what a group is saying and restricted when don't.
According to a "coalition spokeswoman" the white supremacists shouldn't "be allowed to gather because they practice hate speech and seek to incite violence".
Last I checked I could hate whomever I choose (good thing too, otherwise I'd be in jail by now). And as for seeking to incite violence, it's a slippery slope when you start suspending someone's rights because of what they say, rather than what they do.
Our legal system is based on actions -- it's imperfect but it's probably the best we can do. If a guy on the freeway with road-rage says, "I'll kill you!" I can't have him arrested for murder.
White supremacists aren't going to disappear because Villaraigosa suspends their First Amendment Rights -- that just sets a bad precedent for other mayors in other cities.
Over in Gainesville, Florida some folks don't seem to like the town's gay pride parade much either -- but that doesn't mean the mayor should stop the parade.