It was an attempt to deal with the issue of child vigilantism. It IS irresponsible to encourage such a thing. However, Mia had what used to be a killer disease, so presumably she should be allowed to try and accomplish what she wanted to before it was too late for her to have any kind of a life at all. I respected her choice and GA's in supporting her.
Of course, HIV isn't the killer it used to be. There's no reason Mia can't grow old nowadays; possibly even have children if she doesn't mind knowing they'd have to live with a daily drug regimen.