Those who cannot contribute to society should not expect society to support them. And they definitively cannot expect society to also carry the burden of whatever offspring this person has.
I think it is essential that we as a nation work to weed out lesser and degenerate elements. For otherwise we are doomed to fall.
If you're unable to provide for yourself, Then you're unable to provide for someone else. Having children whilst unemployable is one of the most selfish things a person can do, Ideally a person should start a family or have children when they're financially stable or mentally prepared enough to do so.
Some people came from dirt poor families who later went on to change the world for the better.
Some rich families with lots of money give birth to child molesters and monsters who murder thousands.
Point is that you do not know who will be productive and who will be a menace to society.
Middle class families sometimes give birth to mediocre people who will never amount to anything in life. A son who will never do anything important and just die unmarried.
You might kill the person who would invent nuclear fusion or cure baldness or cure obesity.
And even if you kill all the undesirable you will still have child predators and killer sociopaths in your "perfect" society. And they might have nuclear war and your society will destroy itself.
A man tried to create a perfect society in Germany and he failed because usually those who want to purify and cull their society are the actual scum of society. And Hitler doomed Germany and got a lot of white European men killed. Ironic he wanted a white race and just ended up killing Europeans faster.
So my advice is not to meddle because you would do more harm than good.