Easy: it's a matter of moral perspective. People don't necessarily feel the same way about moral issues: gay marriage, different races marrying, when it's permissible to lie or cheat, when a government or even private citizens can kill other people... Others find it selfish to reproduce when there are many children in the world who have no one to care for them and who'll live painful lives for growing up without sufficient resources. There are tons of studies linking early life poverty to lots of serious problems. Some might argue a far better choice would be to adopt or foster first or even exclusively.
Others think it's selfish to bring more humans into the world when we're already nearly 8-billion lusting after a lifestyle that pollutes the ecosystem and pushes record numbers of other beings to extinction. What someone considers "selfish" is an opinion. Better questions are (1) whose rights should take precedence? (2) Are there more net harms to society and the planet overall from forcing people to bring to term pregnancies they don't want? (3) If you can force someone to complete a pregnancy, who owns that person's body--the state? And (4) If you're going to force every pregnancy to be carried to term, are you going to pay to support all those children many can't afford? Related to the last question, is it just to force tax payers struggling to survive themselves to subsidize others' reproductive prerogatives to the tune of three, four, five, six... children?
Whatever your answers (yes, there are other questions, too...), since so many nations allow abortion, people will just find other ways to do what they want with their own bodies. How's the war on drugs working out? How did US abolitionism work out? Good luck forcing others to breed when they don't want to.