What would you say if it did?
If they had been told it was an unlawful assembly, they were protesting without a Permit, that they were trespassing....and were ordered to leave...what would you say then?
The First Amendment does have limits.
Dust blown by a helicopter is far less noxious than Tear Gas.
Besides....the Perps would be identifiable from a mile away as they would look like dust bowl refugees from Oklahoma!