I'm not so sure about the first part. I can see their reasoning behind censoring it - it's not unlikely that it might inspire some people to carry out similar attacks, especially when you look at the disturbing number of people applauding the attacker after watching the video.

The latter part makes a lot of sense and I do believe that Trump knows what he's doing by being a controversial figure. He managed to achieve a sweet spot in controversy where people who like him and dislike him talk about him a decent amount.