I have a simple question for you all. Feel free to post whatever rationals make sense to you. Why did the Evil Mastermind plot his ingenious invasion of the Good People Sanctum?

Threat - real or imagined
Jealousy - Over objects or people

Hows this:
Insanity creating unstable paranoid behavior. The evil mastermind perceives a threat and ironically creates one as his perceived enemy decides he is too crazy to live. They are, however, too late as he strikes first.

I have a few. But they are very mixed/similar.

1. He's jealous because they would never let him into their community.
2. They have something he can never hope to achieve (love, community, real friends etc)
3. He's jealous because as a kid they would never let him play along with them.
4. He's jealous because the leader stole his highschool sweetheart because she'd rather have a "good guy" (Reality begs to differ tho)

How about religious or ethical motivation?
Like believing to be rewarded for one's actions in the "next world".

Or maybe the pain of loss which he blames the community, civilzation
In general or even the whole universe for.

These are all kind of stereotypical of course. But these are the first ones
that struck me.

I guess some evil masterminds just believe that they are doing the right thing.
Example is wiping out a peaceful village because he believes that only by being militaristic and strict control can the village repel invaders. After he takes control, he uses the fact that the village was invaded as proof that his way is correct and reinforces his beliefs and so he goes on the the next town...

I agree with most of these above, jealousy and fear. I'd add that the 'good guys' might have something the mastermind needs for his experiments or plan, and they're either the most convenient place to get this thing, or the only place to get this thing. And they might not even be putting it to good use themselves - it's often the case that a villain steals a relic that he has the knowledge to study while the good guys just have it sitting in a museum. Kidnapping with intent to keep goes in this category too - villains have been known to steal scientists, mages/psions, and potential spouses or 'breeders'. Sometimes it's something that used to belong to the villain - maybe he lived in good people sanctum until they chased him out and he didn't have time to get some of his stuff, or maybe the 'good guys' captured something important when they killed some of the villain's employees, or raided one of his outposts or storage sites, or put social pressure on someone to break a deal they were making to sell the villain what he wanted. Maybe they have a monopoly on dragon breeding and the villain really needs a dragon.

How about for their own good? He saw them causing some harm to themselves (real or in his imigantion) and couldn't stand by and let it happen any more.

That one sounds pretty close to the religious fanatic / cult leader mind set.

True, although I tend to believe that most villains think that they are the good guy. I think even dictators generally believe in what they are doing. It's anyone with a blinding beliefe in their cause really.

Another thought, although it is harder to sell as evil: Something is destroying his kingdom and his people will die if he doesn't take the other one. He could negotiate and rely on the charity of the good people sanctum, but they couldn't cope and millions would die even though some would be saved.