Quite frankly...they are right, you are wrong...
Why? Well firstly, the reason why you saw so much tight clothes on futuristic movies is that EVERY futurist or consultant recommended to moviemakers of the day that such clothes would be worn in the future, and unlike the material available today of the type, it would even be comfortable. Now jump ahead to the year 2000 or so, Under Armor and similar apparel has become more popular(I wore it before it became "trendy"), eventually I see a whole new category of casual clothing that will be...well tight..
RAMA
With obesity rates getting inexorably higher I seriously doubt that the average person will feel comfortable putting every fold of their grotesque, bloated, lumpy bodies on display.
The fit, young, attractive people, maybe. The average person? No. Although maybe that's wishful thinking.
We're talking about a fictional future though, where they don't seem to have problems like obesity. And don't forget that in the case of Trek, we're talking about Starfleet, so they're all fit and trained.
Unless we're talking about the TOS movies, in which case scrap that assertion
