Why, in almost all movies and TV shows with aliens, they are evil?

fear of the unknown? The idea makes it more entertaining for viewers-people would rather watch evil than nice?

Nah, it is more like 50-50, Remember the bar scene in star wars with hundreds of different species drink together. Or our very own lovable Alf her on AM

But I must admit I was a bit disturbed by the Movie Armageddon (1?,2?,3?) where the super-nerd whizz kid throw together an inter-species thought translator and the aliens thoughts comes out as "Hate, kill, torture, enslave, destroy, ..."

This post was edited by JakobA the unAmerican. at October 17, 2017 1:16 PM MDT

Because it's more entertaining than aliens who are all buttercookies and friendship because then there won't be so much action. Maybe nice aliens are more for family movies.

If not so then they wouldn't have a movie.

Like all things wild, they're not friendly. 

I know Protoss when I see them ;)
and aliens are evil because Fallen Angels are evil masquerading themselves as them to fit the times. Today they are Greys. Yesterday they were Knomes, elves and fairies.

Don't believe that is true.

Star Trek, Star Wars, are but two of the many examples where groups of aliens work together for the "common good".