Antinatalism is the philosophical belief that procreation is morally unjustifiable. It applies primarily to human procreation, though some antinatalists apply these principles to all sentient life. Antinatalism as a concept extends far back into human history, and has been grappled with, in one way or another, by many of the world's religious traditions. Modern Philosopher David Benatar sums up antinatalism nicely in a series of axiological deductions, found in his book, "Better Never to Have Been: The Harm of Coming into Existence."
1. the presence of pain is bad;
2. the presence of pleasure is good;
3. the absence of pain is good, even if that good is not enjoyed by anyone;
4. the absence of pleasure is not bad unless there is somebody for whom this absence is a deprivation.
In plain English, if one has a child, that child will hopefully have some pleasurable experiences, but is all but guaranteed to experience suffering. Not having a child is better, because the unborn child will not experience suffering, but will also not be able to regret missing out on pleasurable experiences. Another important aspect of antinatalism, one which is implicit in the above deductions, but could use fleshing out, is the idea of consent. Since we cannot sit down with our unborn future children, and say, "hey, if you are born, you will have lots of fun, but will also grow old, sick, and die; do you accept these terms?" it's best to err on the side of caution by not having one.
Some antinatalists argue that not having a child is morally obligatory not only for the "child's sake," but for the sake of others, such as people and other forms of sentient life which could be harmed by the child's future existence (through verbal and physical confrontations, the child's meat-eating diet, etc.) Others go even further, arguing that antinatalism applies to all forms of sentient life (I don't know whether that means all animals possess moral reasoning skills, or that we should somehow prevent the procreation of all earthly life, which seems a both hopeless and deeply unethical task).
There are some compelling critiques of antinatalism. The first point out the illogicality of deductions 3 and 4. If the absence of pain is good, then, logically speaking, the absence of pleasure is bad, even if there is no one to experience it in either case. That is, it would have been good for my future child to experience pleasure, so depriving them of that experience is bad. Benatar's response is that the deductions are axiological, not logical. Another argument against antinatalism is that most people regard their existence as a net positive, that is, they think their pleasurable experiences outweigh their painful ones, either quantitatively, qualitatively, or both. I am not well-versed enough in religious arguments against antinatalism to find them particularly compelling, so I'll leave that bit to someone else.
I will say that I personally find antinatalism compelling, and don't expect my beliefs to change any time soon (I think even before becoming familiarized with antinatalism, it resonated on a gut-level in my childhood psyche, and that was long before Trump, etc.). I wouldn't be surprised if, as anxieties surrounding declining birthrates continue to emerge, antinatalism emerges as a more familiar concept. "We need to have kids so they can take care of us because we did it for our parents" seems like a vicious hamster wheel, especially considering what the quality of life is now and what it will likely be in the future. Finally, at risk of being too reductive, it seems to me that the antinatalist sees life's experiences as "a glass half empty," while the natalist sees life's experiences as a "glass half full." Maybe, somehow, we're both right.