zlacker

In the cases you've mentioned, people by and large don't form their opinions based on studying historical facts in an objective way but based on what they're told, almost exclusively by their government in these cases. Certain atrocities are highlighted and emphasized repeatedly, others are overlooked or hidden, but rarely because of how bad or bloody they were. World history is basically the history of war and few people consider them all to be bad.

The only school shooters I can remember the names of are the Columbine shooters and I'd say that's mostly due to the fact they were the first in the modern school shooter era (depressing reality). Perhaps that fame helped fuel other shootings, but I can't name a single other one out of the many since then.

I'm sure the fact that we're so used to acts of violence in the US on a regular basis is a contributing factor. At this point you'd have to do something pretty horrendously bad to go down in infamy. On the other hand, if it were an act (without innocent casualties) committed against say a financial, insurance institution or some other disliked entity, they could become a folk hero.