He does have a point on that. Whether it is Trump or Cruz or Bernie Sanders speaking, it is rude and un-democratic to disrupt a speaker in this way.
Exactly. Disruptive protesters are a sign of intellectual bankruptcy. If you have to shout down and disrupt your opponent, that's basically admitting that your own arguments are too weak to stand up on their own merit and that your opponent's words are so strong that they must be stopped.
This is why you have Leftists disrupting Conservatives speakers and rallies much more often than you see Conservatives disrupting liberal rallies and speakers. I'm sure you wouldn't show up to a Sanders or Clinton rally acting the way that anti-Trump protesters behave. Neither would I or 99.99% of other conservatives. With liberals, it's standard operating procedure.