It's not so much a tacit support, as a convenient storytelling device. Trying to come up with aliens who are as varied in personality and culture as humans, and yet all totally different from humans, would be a massive amount of work. Even the best alien-making science fiction writers tend to make their aliens a bit monotone in culture and personality, or else so alien that thay can't really be seen as characters. There are a rare few exceptions, but they're, well, exceptional.

Star Trek wasn't going for realism. It wasn't their goal. The same is often true of "bumpy-head" aliens; they're not meant to be truly alien, just "alien enough".

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort