Based on what? He’s an abrasive jerk, but have we seen him do anything immoral? Don and Roger and several of teh other charactes have been shown doing far less moral things than we’ve seen Jimmy doing.
Of all the bad behavior you’ve seen on this show, you’ve decided that Jimmy’s sole character trait is that he’s vindictive?
I don’t think either “vindictive” nor “doesn’t care a fig” is a supportable conclusion. He was angry at being victimized by Don, justifiably so, and what he did was tell Don that he knew it and he clued in the other victim (Betty). Betty’s reaction is really not Jimmy’s responsibility.
Frankly, I think he deserves a medal for his restraint.
That indicates neither immorality nor vindictiveness. What was actually immoral about getting what he wanted – his success ultimately relies on his own talent, after all – before he said anything?
He had already been injured. Why not use Bobbie and Don for what he could get out of them before spilling the beans? Don and Bobbie have gone ahead and taken what they want. Why shouldn’t Jimmy be allowed to earn what he wants?