It's a major lifestyle change - they know that going into it. But then parents still want to do everything they used to do.
Parents might pay lip service to this fact but I really don't think that a lot of them do know this. They mouth the words but don't really believe that having a kid is going to change their life that much. How they can be so delusional is another topic altogether.
Whats more, they don't care who they inconvenience in order to maintain that delusion.
A lot of the commentors who were parents and agreed with the post are obviously the minority. If well behaved kids in public were the majority we wouldn't be discussing the issue on the boards. I've never understood how parents can just tune out a shrieking child. Maybe they check their hearing and conscience at the delivery room door.