He really wants to use Poke'mon to rule the world, I think.
The "people abusing Poke'mon" thing is an excuse.
He raised N to believe that people are horrible, and Poke'mon are good.
That way, N would support him when Ghetsis took Poke'mon away from humans.
As for the last part of you question... Maybe he is so ambitious he will keep trying.
To get the full story, you would have to play both games, and possibly ask The Poke'mon Company why they made it that way.