Leaving supporters in place and threatening dissenters with arrest is a violation of the 1st Amendment.
Is this discrimination based on dissent legal? The courts might think so. But then they're not only supporting a violation of free speech, but engaging in judicial activism as well.
It's not descrimination. Seperating sides during protests is fairly common. Every seen KKK marches, they tend to have counter protests, those counter protests are shoved to the other side of the street at least. Why? Because: crowd control is LEGAL, and putting people with a certain type of sign in a certain area with people that have similar signs IS crowd control.
Every single person attacking you would rightuflly howl like little squealing piglets if it were the Klintons prohibiting protest signs.
Which makes them hypocrites and quite possibly liars.