^Just because there are other people on a cruise ship doesn't mean you have to interact with them. On the three cruises I've done, I've had almost zero contact with anyone outside of our group. Really it's no different than going to a park full of people, just because they're all waiting in line for a coaster doesn't mean you have to talk to them.
I'm at the point where I'd almost rather go on a cruise than go to a park, if given the choice. They're both fun experiences, but I do find cruises a bit more relaxing. And certainly the food is usually better!
dt