It's true that both sides are monstrous and should be condemned. However, when you have a history of friendly relations with the one side, and it was that same side which just killed somebody, in the incident in question, playing the objective observer and blaming both sides is a joke - or, rather, a PR move. That statement was Trump simultaneously doing the "Presidential" dance and winking at his alt-right supporters. The same would be true if the shoe were on the other foot. Suppose there had been a right/left riot of some kind in 2015, in which the left killed one of the right. If Obama came out with a "well, everyone's to blame" comment, the right would have gone ballistic, and reasonably so.
P.S. Keep in mind, I don't care what Trump says, about any topic, at all, except insofar as it has real effects on things. I have no "moral outrage" over anything Trump said/didn't say re the riot, as the left pretends to have. My only interest in the whole affair is that the alt-right not be further emboldened, that it even retreat, so that we can regain lost ground in the GOP. That's the upshot of all this. Towards the culture war issues that everyone's hopped up about (muh racism, muh diversity, whatever), I give exactly zero (0) $#@!s, one way or another. I think it's a giant waste of time and energy, which is why I want these people off the political stage.