The rational for alien invasions

Hi All,

Sci fi movies often give us the  alien invasion drama . Sometimes this is done in a subtle fashion and sometimes in a not too subtle fashion of big ticket guns blazing type dramas . But in what we could call real life, exactly why would aliens invade.

Let's take a few of the usual reasons given in sci fi:

1. Resources - Yet as we are constantly being told we are approaching peak everything, whether it is oil, gold, trees or fish fingers. But conversely the solar system is a treasure trove of what is for us unlimited natural resources. There's more water on one moon of Saturn, than the entire earth, more natural gas and hydrocarbons on another moon. One small asteroid can contain millions of tons of iron, platinum and other precious or rare earth metals. So no Alien would actually need to go to the trouble of actually invading earth.
2. Genetics - The general plot line here is aliens inter breeding with humans to create hybrids or to harvest human parts for some nefarious scheme or to save their race. Except that unlike Captain Kirk, it is highly unlikely that aliens would be biologically compatible with aliens- even ones with green skin and big breasts - and quite why they'd want to make half alien humans is rather a mystery in this context.
3. The Imperial megalomaniac -  An alien race with a warrior culture that goes around conquering for the fun of it. I could accept this to a certain degree. There is , after all, no correlation between scientific advancement and moral good. If you don't believe me, look at Nazi Germany. The most technologically advanced state in Europe and maybe the world at the time,  for example even in defeat in 1945, Germany was creating fairly advanced rockets and even the Americans and Russians  took German scientists to get them to work, yet the ideology of the Nazis was of course based on genetic purity, eugenics, conquest and  everything else that we would consider to be morally reprehensible .
4. The Invasion from within- I rather like this one because it touches on something that is going from science fiction to science fact- namely the rise of artificial intelligence and thus the philosophical question of what is life? But it is often portrayed as the AI or robots dominating , controlling or otherwise killing human beings. What of something different wherein AI engage in civil rights or suffragette type struggle or action?
5.  The refuges - I can think of two really good films wherein aliens aren't conquerors, but have arrived as refugees and are trying to survive on earth, either by cohabiting with humans or being forced into a ghetto. I  quite like this concept .
6. The original species- I think of Dr Who and the Sirulians /Sea Devils. The idea that there was a reptile type species which went into hibernation when catastrophe struck.  The only thing is I wish that the writers hadn't totally cast them as monsters. I think that they were more sophisticated than that, but it would be interesting to do a reverse of this : what if humans went into hibernation and after millions of years reawoke to discover that insects were know a dominant intelligent speices ? How would we react ?

Well that's all I can think of, can you add any others in the comments or add thoughts to mine?