Why Deitize aliens?

I think people need to open their minds and think about alien life, instead of deitising them? Just look at this planet Earth and the diversity of life; so many species, all shapes and sizes. But when people talk about 'Aliens' its like they're talking about ONE thing.
It looks very likely that the universe is teeming with life, just like Earth. So Aliens will look like just about any shape or form you can think of.

But what about behaviour? Once again we tend to deitise them again- 'why would they travel light years just to abduct; slay cattle??' etc.. - well, all I can say is; dont underestimate cruelty and thug mentalty. Thugs and yobs may be all over the Universe; just because a species has access to faster then light transportation, dont assume they will all be benevolent scientists at the controls. Do banks robbers know how their fast car works? Or how a cell phone/mobile phone work?