Why are aliens hostile?

Eh, i think you have to think about motivations. What would motivate a race to take to the stars? I know we'd like to believe it is to explore and discover, but in reality it's probably due to the need to survive or for some form of gain.

When it comes down to need resources to survive, suddenly you are more interested in taking then you are negotiating, especially when the odds are good that we seem like animals to them.



"We are Groot."

For them Earth was high class michelin restaurant offering delicious human brains.

I think if the aliens were coming in peace they would try to communicate first and possibly request permission to arrive here.

If they show up without warning thats called an attack.

Not only why are they always hostile, but why do they always look like they could not possibly have the dexterity to build a square out of Lego bricks much less create interplanetary craft and advanced weaponry?

Because it's humanity projecting our own violence on fictional beings to explore what happens when technologically and so called civilized cultures discover native/aboriginal cultures.

Because the aliens really represent the communists.

Because there is an alien fleet en route to earth and Scifi films are PSA's in disguise.

Because you can have them behave in any violent, illogical, irrational, inhumane way you want, and not bother explaining why because they're aliens.

Because you can then subsequently kill them all without mercy or hesitation or guilt in the most imaginatively violent, gross, squishy ways you can think of because they're not humans and it wont upset PETA.

Because most of the time, humans invaded other parts of the world and killed local people to take their resources. Or if they didn't kill them immediately, they enslaved them or brought diseases they couldn't fight. Or they brought their religion and brainwashed the locals to force them to accept their fairytales about a man, a woman, an apple and a snake in a magic garden where the landlord is an angry old man with superpowers that he uses at random.

So a film about agressive aliens with superior technology who want to destroy the human race and take over the planet without trying to communicate is not far fetched.