How so? Are you arguing that there would be the same # of abortions if it were illegal? Or are you arguing abortion is beneficial to society in some other way?
I've heard the idea that people will have abortions even if it's illegal as an argument before but I've never seen any evidence that it's true (if you have some please share). It was illegal for years prior to Roe v Wade but I don't think we have reliable stats on illegal abortions. The stats immediately after Roe V. Wade show that abortion instances increased substantially over the first few years after it was legalized. This seems to imply that abortion was less common prior to Roe V Wade and the incidence rate increased as it became more acceptable.
The sheer # of legal abortions makes me think the # would have to be lower if it were illegal. Just cutting off federal funding along might reduce the incidence rate.
Making abortion legal definitely increased the number of abortions. But degrees matter. I don't know of any reliable statistics. You're right that a citation is needed. In the absence of evidence one way or the other, I just go with what seems logical. Abortion is easy to carry out personally in a multitude of ways. Combine that with the high personal incentive given the financial and social ramifications of having a baby... it all leads me to believe that there are not many people that choose to not abort simply because of a law that's practically impossible to enforce.
