Primary reason for segregation is that, whilst doing the job you are paid for, you may one day have to send your subordinates into a situation that is highly dangerous and will probably result in them not coming out alive. Being all good mates around the same table won't make this any easier.
Rank has it's privileges, that is part of the carrot, part of what we work to achieve and has been alive and well in the forces since they first formed up. If it troubles you then don't join.
The only exception, which I found very acceptable, was the all ranks aircrew mess at some RAF stations,(El Adem), when we visited, which seemed to be Officers, WOs and Sgts. A lethal mix for a major PU.