Eh,it is really hard to answer this question,simply becouse 95 % of cartoon villians hardly DID anything to justify their "evil" status.
They just brag about how "evil" they are,then they have an "evil plan",then they build a mashine/weapon,and before they even activate it the heros come just in time and save the day.
It doesn?t really matter if the "evil plan" was laughably pathetic or potentially harmfull to humanity,cartoon writers seem to think that just a mere "tought" of doing something harmfull to society makes a villian "evil".
And those villians who even manage to do an "evil act"(like kidnapping Santa Clause *gasp*) often come of as barely "rude" and "inapropriate".Those are mainly minor harmless villians whos serve as comic releifs.
And then again,maybe I am expecting too much from PG rated cartoons

But keep in mind,those 5 % of truly harmfull and cruel villians can be seen in the old classics.
Like Proffesor Ratigan from Great Mouse Detective-he killed one henchmen for calling him a rat.Probably one of the most disturbing and saddest scene in cartoon history.
Sheriff of Nothingham-he is capable to steal from a blind beggar wthout remorse.It was Robin Hood in disguise,but still..
Horned King from Black Caludron-he murders the good former king(ofscreen),keeps his corpse in his castle,makes the most scary army of dead soldiers,and kills the little dog critter...pure evilness right here
So my answer is : writers should just keep pushing the limits as much as they can
Just my 2 cents