Original sentence: The simple version states that, since those who favor the legalization of abortion are much more likely to get one than those who oppose abortion, and since children often follow their parents' political leanings, that support for legal abortion will decline over time, simply because pro-choice parents will have fewer children than they might otherwise have had
Edited sentence: The simple version states that, since those who favor abortion are much more likely to get one than those who oppose abortion, and since children often follow their parents' political leanings, that support for legal abortion will decline over time, simply because pro-abortion parents will have fewer children than they might otherwise have had