You miss my point - the "assclowns" are going to do it anyway. They don't care about breaking the law or causing trouble.
Therefore, the people who take the time to set up legal demostrations are the only ones being hurt.
How are they being hurt? Because they can't block the entrances to MSG and scream in the delegates' faces? Because they won't be able to mob the entrance that Bush, Cheney et al., will use?
And I've got some news for you: Very few of these groups are peaceful and law-abiding.