It’s the same old reason as how the history is made and written. The Greeks, the Romans, the Pharaohs, the Mongols, and now the West – mighty and the poweful ones always made the history often with aggression.
From Genghis Khan to modern George W. Bush, the invaders were always brutal. Happened it in our past, the super enemies conquered a land with love and peace? Never.
So to imagine a ‘new history’ in the far-future, we naturally sense to experience the same. It’s inherent.
We can hardly imagine friendly, good-looking aliens although we subconsciously agree, if they come, they will be from advanced civilization. That’s one of the reasons they could reach us even before we could establish any contact with them. So the visiting aliens will be very intelligent. Agreed.
The interesting point that hides here: the intelligent aleins or so-imagined advanced civilazation should also be the highest creation in that planet or galaxy. Highest creations will be good-looking, friendly, will bring ‘positive message’ with them when they will reach us. From the first contact on, they will carefully work out to eliminate any misunderstanding that may stand as a barrier in our communication. This could be assumed without any confusion.
Just imagine, we are sending astronauts to a newly discovered planet with less advanced civilization than ours. We will not send troops or robots to enslave them or to create panic there. First thing after making a successful contact, we will definitely explore the planet, its people, faunas and floras, natural resources. As we would like to be stationed there for a longer time, we will explore to overcome climate barriers as well. That’s how it will go on.
But you see nothing of these in the movies. It’s rather more theatrical, brings suspense. We find ourselves as victims attacked by technically advanced aliens, then we fight our way to defeat them, finally the ‘victory’ arrives, now we are the ‘heroes’. It’s cheering, celebrating, gives us a big H-U-S-H, we saved the planet.
We go back home happy.
But then, this makes it possible, existense of higher civilization in the Universe.