On a moral standpoint, humans will never all agree on the same point. Even if we try to use science to back out claims, people will always debate on whether it's okay to have an abortion, whether the fetus is a human, etc.
But there is one way to solve it. One clean way. One way that has absolutely zero drawbacks.
Sterilizing every male newborn.
In the near future (50-100 years) I have no doubt a very simplistic and cost efficient way will be developed to sterilize a man. This would be performed on all male babies and would prevent any and all unwanted pregnancies. Then, when the man is grown up and is married or has agreed to commit to an 18+ year relationship, they are surgically given their procreation ability back.
Who would complain? Men? Upset they can't accidentally impregnant a woman? NOPE. This is practically every man's dream! Being able to sleep with whoever they want with zero consequence (aside from aids and stds). Women? Upset they can't accidentally be impregnated by a man? NOPE. If anything, this takes a big burden off of them!
On top of this, no woman would need to be on birth control. Abortion costs, babies in daycare costs, and pregnancy prevention pill costs would cease to exist. The only cost that would remain is the cost of giving sterilizing surgeries and undoing them when appropriate.
Now once a man becomes unsterile (after he agrees to raise children), there is the risk that he will accidentally get another girl pregnant. Here's how you solve the problem: make men agree on how many babies they want before they become unsterile again, and perform the surgery to take away their procreative abilities after they've had the children. But what if he gets another girl pregnant during this time anyways? Well, make him provide for the child unconditionally.
Of course, I know people will come up with certain scenarios where this doesn't work, so I'll just say this: If you want to find a way around this, then here's my new idea - we 100% sterilize all newborn men for the rest of their lives, and we let all men and women have sex however they want, and when two of them want a baby together, we can use a proceedure to replicate the man's sperm and implant it in the woman. Each baby you have would cost whatever it needed to cost to get this done. If done on a worldwide scale this could be perfected to such a way that it wouldn't really be cost-prohibitive.
I'm making the claim right now, humans will no longer procreate through sex within the next 1000 years.
