It's a tragedy of the commons issue; if everyone decides as you do, the species stops existing, so not having kids is a luxury decision you get to make on the backs of the rest of the species.

Of course having kids is also selfish, as it's bringing someone into this world just to fulfil your biological imperative to reproduce; you create a human being that will (if you don't screw it up) love you for the rest of your life, and your gift to them is this fucked up world, forced to consume scarce resources that may already be gone by the time they're old enough to actually enjoy being a human.