"These people announced on their Internet sites that they planned to come here and cause disruptions, and told their friends."
Sounds like they bragged in public, using their own names. And nothing more.
What's the difference between this and what happened during the 1960's when people wanted to see Dr. Martin Luther King, Jr. speak and were turned away?
Q: How many IBM CPU's does it take to execute a job? A: Four; three to hold it down, and one to rip its head off.