People seem to forget that when Roe v. Wade was passed, the idea that there'd be what we now call partial birth abortions was "absurd."
Well, not really - Some Eugenics believers thought that even up to 5 years after birth, it would be ok to kill your child if it didn't turn out "right"... so...
They use incremental steps, and Roe V Wade was just one of many steps...