I'm all for spouses/ SO's sticking up for one another, but my one question would be, why does the spouse need a co-sig?

If it's someone who's had tough times or (OK) cluelessness, but is now on the way back up, that's one thing.

But if it's someone who is willfully dumb about credit, and won't do what it takes to grow up and get responsible, but now wants a co-sig, I'd be awfully hesitant. If nothing else, it sounds like enabling.