Trump added that for years, those on the radical left have compared "wonderful Americans like Charlie to Nazis and the world’s worst mass murderers and criminals."
One if the left's most significant accomplishments has been to flip the script and convince people that fascist and nazi ideologies are right wing. This allows them to mis-characterize conservatives as evil.
Their most significant accomplishment, which ties in with that, is the indoctrination convincing people that that ideology is the only correct, and superior morality.
Once you convince someone they're fighting pure evil it dehumanizes their opposition and makes it very easy for them to rationalize horrible actions.
I also recognize that the hard right has a similar issue. However, it's usually also linked to a moral code including things like Thou Shall Not Kill. Naturally, everybody is an individual, and can be mislead, or go off the rails.
If we don't re-establish a culture of respectful debate of ideas, the current extreme polarization of the spectrum can potentially take both sides into a dangerous radical realm.
That being said, I've never heard the phrase "The ends justify the means" associated with the right.