The basis for my own argument (not sure about other people) is how OTHERS (generally) view men, women, AND CDers who dress inappropriately for their ages, body types, or the venue. Not just CDers. I think this is what Jennifer was getting at in her OP, unless I misread it. It has nothing to do with how individuals choose to dress based on what makes them feel good. I for one believe that everyone has the right to dress the way they want to.
BUT, if someone goes out in the mainstream dressed way too young for his/her age and/or body type, or in clothing that is sexually inappropriate for the venue, and she is stared at, she must not mistake those stares for admiration. Generally speaking. This goes for CDers AND GGs, and also men, but I think to a lesser degree.
I know that we could put 100 pictures up of both CDers and GGs in various outfits, and if we each voted on what was tacky or not there would be differences of opinion. But, for many of those pics, there would be no argument and this would likely be skirts that are way too short, heels that are way too high, too much skin showing, etc, on someone who is older, or heavier, and who is dressing for a mainstream venue and not a nightclub. These things are difficult to specify using words in posts (as you say, how does anyone decide how short is too short since there are several things in the overall appearance that put together, give the impression of tacky), but it is something that most people just know when they see it.
Last, it is debatable as to whether the CDers who present as men in drag, or who present an overly sexualized/stereotypical version of female, adversely affect those who wish to just blend and not try to call attention to themselves, other than be respected as feminine beings. I think we'd have to take a large survey among the muggles and ask them if they judge each CDer they see on her own merit, or if they look at the more outlandish presentations and judge everyone based on that. I tend to think that each person is viewed based on her own presentation and her own merit, and not based on what others do.
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There's another discussion beginning in this thread about CDers who go out dressed as women but who present as men. I think this is a fascinating topic. It is debatable, however, whether these CDers see themselves as male-to-female crossdressers (as MonctonGirl asks), or if they see themselves as genderqueer (bigender or androgyne ... whatever term might be used), or if they are feminine men who want to redefine men's clothing styles to allow for male feminine expression. Likely all three motives are true depending on the individual. As interesting as this topic is and as much as I enjoy following the discussion, I'd love to see it in another thread since I think it falls outside of Jennifer's scope? I think a lot more people would participate in the discussion if it were in its own thread.