Everyone knows that an energy being which thrives on hate has a totally different internal metabolism than one which thrives on love -- which explains the "never before encountered" remark! Just kidding, LOL. Seems to me those energy beings and all the human looking aliens (that speak English) were attempts to keep the production costs down. But I think Roddenberry was advised that intelligent life, it if evolved on other worlds, would/could conform to human development here ... kind of like parallel evolution. It's having the opposable thumb, I've heard, that was key for human's developing tools, etc.