And some people are meant to be evil, as a part of his plan.

Think about it. Unrepentant sinners are tortured in hell by demons of their sin. But where do the demons come from?
The demons are just the sinners so unrepentant that no will remains in their souls to reconnect with God.

Take gluttony as an example. Even most fatties still have desire left within them to lose weight -- an especially weak form of the virtue of temperance. In their heart of hearts, they WANT to be tortured for their sin, and thus cleansed of it. They feel trapped by the weight of their sin.
And yet there are, among them, those disgusting pigs who are so fat and food-obsessed that they LOVE their sin, through and through, without reservation, and would sooner eat their fellow man's own flesh than lose a single pound.
So when they die, God gives them both what they want: he turns the irredeemable gluttons into demons in the hell of gluttony, which becomes like a heaven for them as they're left to feast on the flesh of the redeemable gluttons, who submit to such punishment as is their secret desire.

It's simple: if you love God more than food, and were just never able to reach that conclusion on your own in life, God uses hell to help you discover that love through penance, and then accepts you back into his kingdom; but, if you're so corrupted, that down to the core of your being, you truly love food more than God, then, in hell, God gives you all the food you could want, and you stay there forever and enjoy it.
Same goes for any other sin, if you truly love the sin more than you love God, with every fiber of your being, then there's nothing to worry about, because yes you'll be condemned to hell for all eternity, but you'll be a demon there and torment more virtuous souls than your own, and it will be like heaven for you. And God made you this way on purpose, because he needs tormentors.

Dear rest of world, how does it feel to know amerilards will eat your flesh in hell