"like the old idea of people should have to take a test to see if they are smart enough to reproduce"
Any idea that compares itself as being like that is bad by default. Kids (all of us really) reflect their environment so we should focus on making the environment better (better education, better job opportunities, more open society, better healthcare, etc) not by putting people in further categories and groups. We already have enough of that.
IMO I don't think you can be born errrm, dumb, it's just that as we grow we learn to prioritise the skills and knowledge that are important to our continued survival and fulfillment of our needs. Next time you meet someone one who you think is dumb take some time to talk to them about what their interests and life experiences are (don't measure them by yours). Its amazing what you can learn.
Anyway we all get addicted to something - other people, drugs, pain, pleasure, being a git.
Facebook has just learned (really quite effectively) how to make their platform addictive exploiting behavioral psychology traits that have been known about for decades. Who cares how it works, just give me the dopamine! I get that.