Protesting outside is fine.
However, on some campuses, they have blocked people from entering the hall, set off fire alarms during the speech, started riots and attacked people trying to attend the speech. They have used air horns and disrupted the speech while the person was speaking inside the hall.
These actions are illegal, but because the campus administrators either agreed with the protestors or were afraid to take action, they did nothing to stop them. In Burkley, they even told the police to stand down and let them riot.
That is why the president is pushing the issue.
If you don't like what someone is saying, don't listen. You do not have the right to stop others from hearing all sides.