If the people promoting it do so in a sincere effort to end human suffering, they're quite misguided.
First, most anti-natalists wouldn't have reproduced anyway -- overwhelmingly the people I've seen who are drawn to the idea are very poorly adjusted and have little or no success in the mating market. Second, to the extent that it actually does prevent births, anti-natalism will only succeed in establishing selection pressures against whatever genetic variants promote the sort of psychological traits that lead people to accept anti-natalism. Selection has been weeding out whatever is harmful to replicative success since life began (and selective processes likely extend back even further than that). You can be sure it'll remove whatever makes people anti-natalists.
The ecologist Garrett Hardin observed this problem in the case of efforts to promote voluntary control of reproduction to stop overpopulation. Inevitably, to the extent such efforts were successful, they would only lead the subpopulation capable of and willing to engage in reproductive control to be replaced by those subpopulations lacking the willingness or ability or both.
My sole reason for being an antinatalist is to reduce suffering, not impose more of it. I care a great deal about children. Over 500,000 kids in America and millions across the globe are crammed into orphanages in desperate need of forever homes. Meanwhile, folks keep creating new sentient beings who must struggle with the burdens of existence while other kids who need mommy's and daddy's are denied. Stuff like this bothers me. I can write an entire encyclopedia about why I think natalism is wrong. But that was just one example.
I'm 35, very maladjusted, on SSI. I never had a job or a drivers liscens. I still managed to get married. It lasted for 3 years. Due to my mental health issues, everything fell apart. In the beginning of our relationship, my now ex wife and I discussed having children. I was against it due to my stance in procreation. I also had 3 very short relationships prior. I had a horrible childhood which led to an even worse adulthood. I was raised around children who had it way worse then me. Most of them grew up to procreate, then neglected their kids. So maybe I do have a bias...or maybe my own struggles and what I observed made me more aware of our implosion.
I'll admit, many people have had wonderful childhoods and are glad to be here as adults. I respect that. I am not saying "ban natalism". That would be assanine. I'm saying people should take a very hard look at the ethics of it all, the realities we must face, and were we are headed as a species and ask - is it worth it?
Like I said - you can't have natalism yet deny people the right to die and call it a fair system. Many on this site, including myself, can relate. We were born because our mothers decided to carry us to term. Now we are trapped here with no peaceful way out. What sort of crap deal is that?
EDIT: Plus to me, having children is like gambling but with someone else's life. You never know if the child will be healthy or end up like Ted Bundy or severely disabled. I'm my opinion, it's best to roll the dice with your own life.