It still sounds sketchy to me. Threatening to leave is giving your employer an ultimatum. Personally, I think the rational response to this is to placate you, find your replacement, then fire you. If you actually have issues with your work environment, you should address those head on without the threat of leaving the company.
I'd like to think (and try to only work for) people would be professional enough on both sides to realize that not everyone (either side) is going to be happy 100% of the time but a) both sides can work on it to make it better and b) if it doesn't work out, try to be supportive of each other so that both come out stronger overall.