Murray is never having kids.  And if he had a say, no other wizard would either.

He does not, presently, have a say.  He's not ever going to get a say if he goes for voluntary euthanasia at age thirteen, which, it's not like he'd been seriously considering but he sure does think about a lot.

One night, a bit after his ninth birthday, he stays up late, curled under his duvet, and spends some time trying to actually evaluate the idea instead of just mulling it over as a background thought, as a cozy lie for whenever the thought of getting eaten or pushed into the void or eaten and not dying ever ever ever aaaaaaa

 - becomes too much to bear.

His ultimate conclusion that night is that he has a moral obligation to try and keep living.  Not for his parents or his remaining siblings or for himself or for anyone else, but for everyone else.  It is his solemn duty to try and use his life, however short and abruptly-ending it may end up being, to try and - not ameliorate the issue but fix it, because it seems like he's the only one around who cares enough in the right way to try in the right way.

He hardly lacked diligence before but now he applies himself even harder, and whenever those thoughts become too much to bear he bears them anyway, and instead of comforting himself with the idea that he just won't have to deal with that, he strengthens his resolve that he will make sure that someday no one will have to ever again.

(Mundanes are fine; mundanes will be fine once there aren't wizards allowing the continued existence of mals and making more of them, and of course the maw-mouths need to be taken care of ahead of time, it's out of the question to leave any of them intact for a second longer than is absolutely necessary - )

He probably won't be able to ensure that literally no wizards worldwide have any more children while still getting to live out the rest of their lives in happy peace.  But there are other options for making sure they don't get a share of the future.