I agree completely with Sylvia.
We had 3 male and 3 female Paradise fish in a 48G tank and had no problems whatsoever with them. Nobody had ever mentioned keeping males together would be a problem until Sylvia pointed it out. As they were all behaving well, we decided to keep them all and thought we were just lucky! After about 4 months the males started to become aggressive towards each other and fighting amongst themselves. They also became aggressive towards the females.
We ended up taking them back to our lfs and then it was pointed out not to keep males together!
Sometimes people are lucky but the problem doesn't always arise straight away. I'd certainly keep a close eye on them.