As wwDavid said, I really thought you were writing about me. (You're not faking the bit about being a pharmacist, are you?)
In all seriousness, I am in your husband's situation now and have been for some time. A couple of distinctions are that my wife does not make the money you do. She does online teaching, more for enjoyment than anything, I think. She also pretty much spends every penny she makes on "fun stuff" for her and our kid. So I am the breadwinner, and I have to think long and hard about calling it quits.
That said, we do have a goodly amount saved and could go a number of years without me working. And, to her credit, my wife has encouraged me to quit or go part-time. What's stopping me, (and I suspect your husband)?
First, you're exactly right about men feeling a need to work, especially in the less progressive states and communities. Men also don't like to be perceived as quitters, and we don't like to "let the bastards win," which quitting would seem to do. I try hard to look past this, but the bottom line is that I spent a lot of years going to school and even more learning my professional afterwards, and I just hate the thought of chucking it all.
We also have a fear that you must either stay in the game or retire. If you call it quits and take a hike, there's some chance that you will be viewed as someone who couldn't hack it, damaged goods that no one will want to take a chance on again. There's also the concern that you will become too rusty to make a comeback if you sit it out too long. I think these fears have some merit, but your husband and I are probably over blowing them.
I'm also genuinely terrified about the economy and the future of the US. I don't see my field (law) EVER getting back to where it was in terms of financial security, and I have significant concerns about whether the country's job market as a whole will ever recover. I've also seen our portfolio hammered by two horrible bear markets, and I know that could happen again at any time. Just think, mideast turmoil, oil/gas shortages, you name it.
Finally, I don't want to "use up" everything I've saved and cut it close financially, I want to have funds available for family if they need it, and I personally feel an obligation to leave my son something.
So all of this combines to make a perfect storm of fear and a feeling of being trapped. If it's any consolation, you can appreciate that you are married to someone who is obviously very responsible and wants to make sure the family is well provided for.
My suggestion is this:
Get your husband to take 2 or 3 months off. Given the symptoms you've listed, you can probably get a doctor to order it, thus bringing it within FMLA protection. Get him some much needed R&R and perspective. He probably should also seek out some counseling, as that can help him see things from different angles, put some perspective on his fears, etc. If he's not on an anti-depressant and/or anti-anxiety med, he probably needs that. While off work, he can calmly explore other possibilities, including things that he probably now thinks there is no way he could find the time to do.
After that leave period, he will probably at least feel sufficiently recharged to go another several months or longer without feeling quite so miserable. If the feelings return just as severe, then he will know that it is high time to quit for good.
Last thing. Try to remain supportive. I know it gets hard and frustrating, but the compassion and support of a good wife can mean all the world, especially if he has no good friends at work.