SF clothing fits certain particular stereotypes. Having watched over 1000 sf tv episodes in the last 3 years (and taken notes!) I feel I can speak somewhat with authority.
Skintight is a favourite, both male and female (Gil Gerard's outfit was often as tight, and often much more skimpy, than Erin Gray's).
Star Trek TNG onwards has some serious fashion faux pas, from Wesley Crusher's Reader's Digest home knitting patterns, to the identical outfits worn by some s1 pleasure planet lot, where the men were in more danger of spilling out of their clothes than the women (I say clothes, but pouch would be a better description). It always amused me too that while then TNG men's uniform got more and more roomy, to accomodate those expanding waistlines, the ladies uniforms remained figure hugging. Naughty (they should have brought back those totally skintight suits from S1-2 for all, including skirts for men!)
The big transgressor is skintight but low cut, showing massive cleavage. Take a bow Deanna Troi, Chiana, and Trance Gemini.
Skintight and leathery, therefore serious fetish, became popular in the 90's, culminating inthe Matrix after which everyone wore leather coats (Farscape, I'm looking at you).
Giant collars are also a mark of SF, starting with good old Ming the Merciless, but common throughout Star Tek and Space 1999, culminating in an S3 ep of Blakes 7, where the collars were almost higher than their heads, and at one point there was a fire crew that seemed to be dressed as extra strong mints. B7 though was a big offender when it came to dressing their sci-fi peeps in old Robin Hood outfits - usually with MASSIVE sleeves.
Thing is I could believe Wilma Deering's outfit (if you take into account Buck's), but Seven of Nine and T'Pol's S1-S2 chicken fillets are pretty unforgivable.
Also terrible are high heels on 'action girls' - all shows seem to offend in this area, with the possible exception of BSG.
Speaking of that, Six's red dress is far more justifiable than Deanna's cleavage or Seven of Nine in general, as it define's the character and makes the point.
It seems the current 'look' for women between 20 and 40 (going by my colleagues and the folk I pass on the way to work) is form fitting and demurely attractive, though not overtly sexual. I only see massive cleavage on a Friday or Saturday night.
So, to get to the point in the wandering rambly waffle, cleavage is only acceptable on 'party' outfits, but form fitting (as opposed to skintight) is totally justified.
As an aside, and it is a different genre, but has anyone watched Legend of the Seeker? While there is some fine cleavage based fan service for the boys (and the odd fetish leather suit), the ladies are treated repeatedly and at length to the heroes well muscled physique.
Nowt wrong with fan service as long as it treats all folk equally.
