Well humans are almost always the last line of defence. If you take a look at movies like I-Day, Transformers and Battlefield Earth etc. Humans are the superior race in the universe. 
You mean Solar System as the biggest rathole that every final battle takes place here? I agree.
Normally during the peace time when traveling aliens jump to hyperspace to skip this boring rural region of the galaxy.
About this mental virus. It was already invented on Earth more than 100 years ago. It's called socialism. It slowes and reverts every civilization from development, so for instance as a result US is no longer capable to lunch astronauts into space. And instead of looking for new resources in space they waste taxpeyer's money to fight with inevitable global warming, volcanos, global cooling and growing population through more taxes, bureaucracy and birth control?
