Most of the time when people say they have an unpopular opinion, it turns out it’s actually pretty popular.
Do you have some that’s really unpopular and most likely will get you downvoted?
You’ll just end up like China with millions of undocumented children, mostly women. Children who are local get to go to school as long as they are registered to live with a local family, so there is no impediment there. Also you will have tremendous flouting of the law unless you create a perfect sterilizing agent that is reversible and deploy it en masse.