No, I don't think cruises are for adults only but I don't like being near the little snot-factories. My kids are grown and I don't really like the prospect of being in the cabin next to a screaming kid.
The same goes for being on an airplane. Most of us have a sense of dread when a child is in front of us or behind us.
I'm just not afraid to say it. Leve them at home and allow your fellow cruisers to enjoy the escape of an infant-free vacation.