You are of course free to do this, but you bring up 3 points, let's inspect them. I'm assuming you're being underpaid by $6k or more a year.

1: Fair, but should you worry about getting fired? Even if you are in danger, if save 2/3 of your paycheck for every month of work you can afford a month of unemployment with no adjustment in lifestyle, that's already large, but you could increase this padding by having a market-conforming salary.

2: Is this worth $500+ a month to you? If so, I'd suggest you seek a therapist, because that is a much healthier long-term way to solve this problem.

3: Well yes... You can also try to not worry about it while earning more.

A nice company, normal hours and a good and interesting job is certainly worth an enormous intangible amount!

However, all things being equal I would not recommend you keep being intentionally underpaid.