The joke is that there are Congressman and senators who are trying to outlaw abortion, and women say “the government is telling a woman what she can and cant do with her body”. By issuing this challenge in the first panel, she is showing that really the abortion issue is about what is currently called “Slut shaming” than actual rights of people. When its turned around on men, its suddenly a shunting of rights.

I’ll agree that it’s not equivocal because if a man does not let out his sperm through the traditional means(masturbation or sex), it will do it automatically in sleep, or when you urinate (it has a limited “lifespan” and has to go somewhere to be flushed out.) But its good for pointing out the discrepancy in the thought process.