First, I was against doing intentional harm. I absolutely think s/he should walk away, but making enemies doesn't solve any problems and certainly could create some.
Second, you seem not to understand the difference between "breaking the law" and "getting sued". Intentionally screwing over a company can be both legal and lead to a lawsuit that you end up losing.
1) You are critical to the company's success yet..
2) They don't want to compensate you to your liking..
3) So you walk. Yes, this is meant to intentionally hurt the company with the only lever that you have (your skill set and institutional knowledge).
You working for this company costs you opportunities elsewhere.
You're convincing yourself to stay because it "doesn't solve any problems and certainly could create some." Your vague fears are holding you back.
But if we get rid of these vague fears, here's what we know is certain:
1) You're critical to the success of the company.
2) But you're not going to be compensated to your liking
3) And you're costing yourself other opportunities by sticking around.
Quit being scared, look them straight in the eye, and say "I am walking unless I get X,Y,Z." If they say no, then kindly resign and don't look back. Bring on the lawsuit (highly doubtful).
There is no way you're going to end up getting sued for leaving, intentionally or not, regardless of your intentions if employment is at-will (and most likely it is).
Second, you seem not to understand the difference between "breaking the law" and "getting sued". Intentionally screwing over a company can be both legal and lead to a lawsuit that you end up losing.