no I think its extremely infantile behaviour to use light sarcasm when discussing serious matters

I wouldn't agree. Here the sarcasm isn't used to belittle the victims but to mock and shame the perpetrators.

Yeah I bet the Qatar monarchy is absolutely red with shame because someone offhandedly made a sarcastic comment about them on the interwebs

Sigh. When someone shames powerful people on the internet they are generally not expecting the people in question to see it. (Well, except it's about Elon Musk :) The intention is rather to raise awareness among the general public.

What happened to not using sarcasm when dealing with serious issues? Seems like pretty infantile behavior to me.

Sarcasm, irony and euphemism are modes indirectness, like gallows humour, to help us talk about the horrific without the equivalent of burning our eyes out staring at the sun. It's a coping mechanism.

Sincere and explicit statements of horror have paradoxical outcomes because such words wear thin. They are overused by the disengenuous to wound others. The sincere are forced onto a semantic treadmill seeking different ways to express themselves.

Infants are not sarcastic. Even older children struggle with it.

So, in reality, sarcasm is actually a very grown-up thing to engage in. That doesn't necessarily mean one should.