This isn't normalisation, it's celebration.
I'm not going to be coy about why they're celebrating him either: The pro-gun community spends hour after hour theorycrafting about how they can shoot people with their cool guns and get away with it. Kyle is being celebrated for finding a new "get out of jail free" technique that specifically targeted undesirables for murder.
That's all there is to it. They shower him with fame and money because he killed BLM protesters with America's favourite gun. It's his reward.