Yeah, this subject has been discussed to death. But I think that sometimes people get turned off when they read opinions based on research on the topic vs. opinions based on actual experience. I think both types of opinions are valid, but maybe someday I'll start a thread for people who have actually cohab'd extensively to give their stories. Here's mine:
In the late 80s and early 90s, I kept communal groups of corns together. These groupings were random, and I had males with females, and juveniles (but not hatchlings) with adults. There was no public internet, and the limited literature supported the practice (specifically, Michael McEachern's book). I saw lots of signs of stress that I didn't recognize as such, e.g. regurges, refusals, and jerky/twitchy behavior. I also saw a great deal of male combat. This was VERY interesting, but the smaller males really took a beating, though no real physical injury resulted.
Then I had an underaged, under-sized female Miami lay eggs. I was so inexperienced that when she stopped feeding prior to the lay, I took her to the vet. The vet was terrible, said she was dehydrated (didn't even recognize her gravid condition), and actually hydrated her with with a hypodermic needle! A couple of weeks later she laid about 20 small eggs. She was so skinny and weak afterward that I really thought she was going to die. She survived, but she never really bounced back.
I did a terrible job incubating those eggs. I think five actually hatched, but one of them was very weak and died. I kept the other four together in a 10gal tank. I was fortunate that they didn't eat each other, but then I made an unfortunate move. I bought another hatchling at a pet store, brought it home, and put it in with the other four (hey, there was more than enough room). The pet store hatchling had mites and of course they were spread to the other four. What a royal p.i.t.a. cleaning up that mess! That was when I started figuring out on my own the value of separate housing and quarantine.
And almost a couple of decades later, I don't even entertain the idea of cohabbing. Plastic tubs are cheap, so there's just no need. I still think that an experienced keeper can pull it off under very controlled circumstances, with select groupings, but I'm not going to do it. But even if I had no experience with the practice, I'd heed the warnings of some of the very experienced members here.