That's not the trolley problem. Here's an explanation of what that is.

The antinatalist version of the trolley problem would be whether it's permissible to impregnate someone if it led to five other people not being impregnated, or something.

Yeah so when you're talking about someone who doesn't yet exist, there aren't direct sacrifices, so I would reformulate what you are saying to something like this: "When choosing to reproduce, you are gambling on giving rise to a happy life at the risk of giving rise to a miserable one."

I don't know if this is exactly what you had in mind, but I suppose you could say that by making this gamble, you are making it on behalf of the person you are bringing into existence, and only they should have the moral authority to have made such an important choice. But we are happy to let parents make many decisions on behalf of their children, and don't give children any moral authority. And the non-existent can hardly make such a choice for themselves. Indeed, it is only after giving birth to and raising a child to adulthood that we give them their full rights and freedom of choice; prior to that important choices are made for them, and we find this acceptable.

An alternative approach is just to more straightforwardly argue that taking the gamble is ethically wrong because the possible bad outweighs the possible good. This is where you would do well to deploy an asymmetry argument. Check the link I sent you.