It depends on a few factors, the main one being their maturity. If my kids have demonstrated a capacity for/tendency towards rational thought and mature decisions, I would have absolutely no problem with them doing just about anything they want to do (not just with games, I would allow drugs, sex, etc). I would make sure they know any and all consequences of their actions are entirely on their head, and probably try to discourage them, but I would not simply disallow it.
I don't actually have kids though, so this is all conjecture. I can't honestly say I'd live up to that ideal.