I've kept many snakes as pairs. Eight snakes in the same cage is a bit much, IMHO.
What you are seeing is the result after two or more snakes are put together and proven to get along. Sometimes they prove not to get along and must be separated again. You haven't seen that.
The operative word is NEW. Don't put a NEW snake in with your established snake. For reasons which you already know.
Corn snakes and rat snakes aren't known for eating other snakes. If fed separately, there is little danger of one eating another. But that's LITTLE danger, not NO danger.
Corn snakes are among the most good natured snakes there are. Once through quarantine and feeding well, many can be kept in pairs or trios without any problem. That is MANY, not ALL. Because some do not tolerate the stress of living together and must be separated. Once I was given a boa constrictor because she was on a hunger strike. Just getting her away from her cagemate and into my individual cage with a nice, tight hiding box was enough to calm her and get her eating again. And boa constrictors aren't as high strung as many species I could name.
When you see two or more snakes together, you are seeing them either before problems have surfaced or after the problems have been worked out. The snakes have proven to be able to handle the extra stress. None has passed pathogens to any other, or if one has, the other has not been severely affected. There hasn't been any uncontrollable urge to eat a cagemate. And so on.
