Pfft, if women had the option to quit partway through I'm sure they wouldn't handle it very well either.
The fact is they make the decision to get pregnant knowing they won't have to face the consequences for another nine months.
It's like getting strapped into the roller coaster vs climbing up that first big hill. If you have to decide while you're safely on the ground you say: "Heck yeah, looks like fun!" But 5 minutes later right after it starts you are screaming: "LET ME OFF!!!"
Only instead of a fun roller coaster ride it's gradually increasing discomfort followed by hours of pain and blood.
They did a test on two guys where they strapped electrodes to their abdomen to simulate the pain of childbirth: https://www.youtube.com/watch?feature=player_embedded&v=ZlsPXpR2ORU
You might need to enable Closed Captioning to get the subtitles. But basically the one guy took it like a champ, and the other one took painkillers and finally bailed.
And that's was just for the heck of it. I'm sure if he was actually responsible for producing a baby they other guy would have stuck with it too. (And of course if it were a real labor, he wouldn't even have the option to stop.)
Men can handle extreme pain if the situation calls for it. Or even to win a bet.
Although of course men aren't quite equipped the same. So if men WERE going to give birth, they'd face the issue of trying to squeeze something the size of a melon through a hole the size of a BB. So it would be loads worse.
But hey, Hyenas don't always die from it.