I agree that there are quite a few nutters out there...maybe even a few here (not pointing fingers, don't get in a huff people ; )
I really think it's a mix of what you say above, some people make poor financial choices, some have mental issues, some have a fixation with the BRAND, some that qualify for all 3. And some people are mentally stable but just plain incompetent. I personally can't imagine choosing WDW over my mortgage or anything else of financial importance but people do it all the time with other "additictions" like alcohol & gambling. There's moderation in all things in life and there's the extreme's. I could visit DL a couple times a month but in no way could I go every day like some nutters do.
That is absolutely true.
The thing is many folks don't see or believe that addiction to Disney (or UNI) is real and can be just as harmful and destructive to a person as substance abuse, gambling, ography, eating etc.
The term addiction isn't by definition something good ... even if say you're addicted to pie!