There's one huge downside to this: eliminating poverty by reducing population leads to aging society, which leads to shitty pensions for retired workers, higher taxation, higher public debt, etc, which in turn leads back to population reduce.

Basically, birth control leads to a slow death of civilization. The most tragic thing about it is that you can't do anything about it, as denying women the choice would be violation of their human rights.

Therefore, advanced societies are doomed to die out and be replaced by more primitive ones. Which happened few times in history (e.g. Roman Empire) and is already happening again in some part of the world (e.g. EU immigration crisis)