honestly that guy might as well have been a mass murderer
Do we have definitive proof? Also, even if true, Brian Thomson was just a cog in the machine and taking him out doesn't change the trajectory of American healthcare.
By contrast, Hitler had published his genocidal intentions in pretty unmistakable form, was on the verge of seizing power and was the leader and figurehead of a movement which was fully geared toward him individually. In the case of Hitler in, say, 1931 or so, it was reasonable to assume that his movement would crumble if you took out one single person, and that he would lead the world into disaster if left unchecked.
Nobody in their right mind can say the same about Charlie Kirk or Brian Thompson. Even with regard to Trump, it's a huge stretch to make this argument, considering that he had already been in power before and didn't abolish democracy, didnt't commit genocide and didn't start new wars.