It's just meant to be an observation. Like "what could go wrong!".
I also don't mean to imply in any way that the victims in *this* shooting did or said anything that was even slightly insulting, let alone a reason for someone to seek revenge on them.
I like America and Americans but I think it has some challenges that it needs to address and right now, the killing of it's own citizens seems to be high on the agenda.
Claiming that is Anti-American is a bit lame IMO. I see those claims most often being an attempt to silence an opinion. Anyone who tells you that "something is wrong, you can do better" is not Anti-American unless you are incredibly insecure. If you want Anti-American go see ISIS ... or Trump, LOL. I think there is a definite cultural difference with how UK people talk about their friends - what you interpret as insults is typically friendly banter. But I apologize if you find it insulting.
BTW: I was in America just last week and down in Texas no less (San Antonio). It was nice (but HOT!). I didn't get shot so that was nice.