There are far too many humans already, why not limit the numbers being born in a beneficial way? that rewards to intelligent, fit, healthy...people that can improve the human race rather than supporting more kids who never learn to read or write, claim benefits then squeeze out more kids, (this might be a bit contraversial) who 90% of the time don't fall too far from the tree.
Also is it more morally right to prevent hereditary illness being passed on than to allow someone to be born into a horrible existence, of mostly suffering. Look how many people want to try and make suicide legal becaus