I'm a breeder and have 42 rats. Other pets include 2 mice, 2 hamsters, 3 dogs, a cat and a horse. Between working at a bar 3-4 days a week (all night, so I sleep all day), giving a riding lesson every Monday in a town 1 hour away, playing groom for two horses twice a month, exercising my horse and still trying to juggle something resembling a social life, I don't have a huge amount of time for my rats. But they're happy, healthy and they all live in same-sex colonies so have friends to keep them company when I'm not able to.
One of the many reasons it is recommended to keep rats in same-sex pairs or groups is so they can have a constant play-mate, even when their owner can't be there for them. If anything, it makes you a more humane rat owner in that you have friends for your rats and don't just expect them them to live out their as singles.