He did kind of shove them back when they were grabbing him, so I don't think he is entirely innocent. However arresting him his ridiculous. I don't know what happened, but what normally happens if after taking the person down the station they leave them there over night or whatever then release them without any charges.

As for it being a public forum. A forum implies discussion, not a lecture. So when you open the floor to questions, you put yourself at risk for people asking questions you may not like, and possibly even ranting.