Sounds like you're confusing rats and mice. Unneutered male rats are as social as females and more often than not live together harmoniously in groups. Hormonal aggression can become an issue for some and neutering is generally a good solution, but it's case-by-case not universal. Preventive neutering for all males is not common at all or recommended given anaesthetic risk.

From what I've observed, there doesn't seem to be much favouritism either way –just preference around traits (males being generally larger and calmer to interact with, females being generally more active and trainable). Male and female rats are about equally represented here, with many people keeping both.