[pimmen89]

The problem with your argument is that it can be applied to births as well; if we allow mentally disabled people to be born, could we not then argue that the benefit is one sided and not the society they're born into?

Basically, what you're arguing is that a person's right to pursuit of happiness is lower than a society's right to flourish. And, also, that the society has the right to choose what types of people are undesirable (by criteria that goes beyond "do you follow the law", because merit and culture includes so much more).