"There's no actual death in SJA though, which I think is a key difference."
Yes, but not in a good way.
Take two westerns. Consider, perhaps, Sturges' Magnificent Seven (PG, as a legacy of originally being A) and Eastwood's Unforgiven (15, as initially certificated). In both of them, there is killing and injuring, both with guns and fists.
In M7 it's consequence free: people are shot, fall to the ground, and either get up (it's only a flesh wound) or don't. But you know that when the cameras stop, they all stand up and have a beer. The same applies, more so, for High Noon (U). The idea that actions have consequences is completely obscured.
Unforgiven, Eastwood's masterpiece, continued the concept of the revisionist western, and is quite clearly violent. It portrays nasty, violent people as nasty and violent, and it's visceral in the way that the violence hurts. It's a deeply, profoundly moral piece. It upset some people who watched it, and so it damned well should.
I don't think that violence should be made glamourous. Peckinpah was attacked when he made The Wild Bunch because it showed people dying in a way that wasn't photogenic (although later, of course, he was criticised because it's too photogenic!) I don't think children should be shown prettified violence: if you are prepared to show them fights and killings (which appear to be a staple of cartoon programmes, which were mostly banned chez nous) then you should be very clear in your mind why you wouldn't show them Reservoir Dogs alongside (which, for the record, I wouldn't).
There's a film theorist who says that she'd rather they saw neither, but given the choice she'd show her children Reservoir Dogs over Bambi. I think she's exaggerating for rhetorical effect (say it isn't so!) but she makes a generally good point: if you won't show children realistic violence, you shouldn't show them it tidied up, either.