Ignoring the microethics of the situation, look at the broader view. We're running out of synthesized phosphates for fertilizer. No fertilizer means less crops, means less food, means less people. The Earth can naturally support about 1-2 billion people (assuming phosphates are the limiting reagent). We've managed to boost that up to close to 7 billion through mineral-derived nitrogen/phosphate fertilizers and better healthcare.
The world's supply of mineral phosphate reserves will dry up in 70-300 years, depending on which experts you listen to. At that time +/-20 years, there will be massive famine, war, and a sharp decline in population.
Let's assume that there is a theoretical way to prevent the phosphate crash, or to at least reduce its impact, or to preserve civilization. The longer we have before the crash, the longer we have to come up with a solution.
The more people born, the more food is consumed, the more fertilizer is used, the quicker the crash will come. The fewer people born, the longer we have to solve the problem. Or maybe we could even reduce population below the critical point.
But from the long-term perspective, abortion or anything else that slows the birth rate is a good thing.