I'm not saying whether it's a good idea or a bad one, but isn't the fact that it's a defacto standard, sort of the objectors' point? Yes, you're right: it's a long-established tradition, with deep roots going back to when the computer room was a total sausagefest. I can't playfully slap the secretary's ass and then get off the hook by saying, "oh c'mon, we dudes have been doing that forever! It's always been like that. Quit trying to change our culture."
Changing the culture is an explicit part of a lot of peoples' agenda, because nobody really likes the damn computer room sausagefest (we just don't know what to do about it, which is why I really have no idea whether or not the picture is really a problem).