“Everyone who’e for abortion as already been born,” said Ronald Reagan (1911-2004) in a September 1980 presidential debate. “It’s a funny thing, but all those people who favor birth control have already been born” had been cited in print in 1965 and quickly became a popular joke. The authorship of the saying is not known.
 
 
Google News Archive
11 January 1965, Millwaukee (WI) Sentinel, “Yes, It’s Great to Be Alive” by Buck Herzog,
MONDAY’S WASH…In his favorite analysis bar the other day Cliff Duffy tuned in on a conversation about the recent Gallup poll which said that 81% favor making birth control information available. He heard one man make this observation: “Looks like the only ones in favor are the people who have already been born.”
 
7 July 1965, Pocono Record (The Stroudsburgs, PA), “SportScope” by Ken O’Brien, pg. 11, col. 2:
One Boston columnist summed up this topic quite well when he wrote: “It’s a funny thing, but all those people who favor birth control have already been born.”
 
Google News Archive
29 January 1967, Modesto (CA) Bee, “My Favorite Jokes: by Totie Fields, Parade magazine, pg. 6, col. 3:
Have you ever noticed that most of the people favoring birth control have already been born?
   
Google Books
Presenting Mark Russell
By Mark Russell
New York NY: Everest House
1980
Pg. 134:
The Supreme Court decision legalizing abortions immediately transformed the subject into a political issue. The position I took was that those favoring abortion were people who had already been born.
 
Google News Archive
22 September 1980, Pittsburgh (PA) Post-Gazette, “Debate contrasts Reagan, Anderson,” pg. 8, col. 3:
A few moments earlier, Reagan had dryly observed that “everyone who’e for abortion as already been born.”