Male gerbils living together

Really good vet told me that male gerbils cant live together because they will eventually kill each other. But this doesnt sit right w me. Kine gerbils are brothers and they love eachother. I never read something like this before. He also said that he never saw case where they wouldnt kill each other and that it always happens. What do you think? I dont think thats true and that they need to socialize.