Marital stuff is really hard to advise on based on a few words on the screen, but here's my .02, for what it's worth. Men can seem irrational when it comes to job-related things. They really have it ground into them from an early age that they are supposed to support their loved ones. Doing anything that might threaten that is scary to them in a way that it's hard for us to understand. And I can only imagine how difficult it must be to be supporting a whole family with no one else earning any money - can you imagine the stress if that was all on your shoulders all alone, and one wrong step in an economy rocketing into recession could mean disaster? Maybe thinking of in that extreme sort of way a little bit would help you when you talk to him, if that's the mindset he's coming from (of course I don't know if it is, but that's the kind of thoughts that keeps my husband awake at night - and I work! But he takes it all more to heart. It's not just money, it's manhood, you know?)
Personally, given the uncertain state of the economy, if he works in any industry that might be seeing recessionary times (banking, real estate, construction, manufacturing) I think he might have a point - I think you should start your own job hunt as soon as possible. That would show that you are also taking the change of job seriously (since you said that his change would require you to work too). Of course if you do that, it becomes non-negotiable - he will have to make the change, because a family with 2.5 jobs would be an unhappy family! Good luck. I think the first step when a marriage has these stumbling blocks is to really try to talk honestly with each other - but it can be so hard.