On Star Trek it seems silly because they have aliens walking around with human feelings. What human emotion would an alien find impossible?

Vulcans represent our rational tendencies.

Klingons represent our violent tendencies.

Ferengi represent our materialism.

The Borg represent our striving for efficiency.

... It all just shows that any ideal taken to extreme is flawed.

(i think the Romulans are the closest to "full" human emotion wise - though they share ancestors with Vulcans) This post was edited by Walt O'Reagun at September 22, 2017 6:21 PM MDT

I rather depend on what kind of Alien.
I thin klingons would have problems with mercy
The Borg would have problems with loneliness

and so on, each species having its own strengths (or weaknesses).

Then again some may have emotions we do not recognize as feelings, eg: the terrible feeling of having accidentally crushed the egg you just laid. This post was edited by JakobA the unAmerican. at September 22, 2017 2:48 PM MDT