0) It's a numbers game. Any (stated) "purpose" can be profitable, in the aggregate, if the underwriting is right. (My mind flashes to Rodney Dangerfield in 'Back to School': "If the roast beef is right, they'll be back.")
1) On "bullshit" (and thank you for using my favorite technical term of art) - and keeping in mind Rule Zero - it's not necessarily bullshit advice, but it's not necessarily correct advice, either. I believe your intuition is generally correct, from a behavioural finance perspective, but, at the same time, I think you've got to accept the nature of the game and that most people who borrow money don't think like you - otherwise they probably wouldn't be borrowing money (paying more now to do something for which they've not yet earned the money).
2) "Deadbeat losers" is a bit harsh (and this coming from someone who loves to say unpopular, but true, things). A lot of people don't think longterm. Most people wind up living beyond their means by stacking up a whole bunch of "affordable monthly payments" - some come to realize that that's a great way to become an indentured servant to one's credit card company and then look for a way out of it; that's to be applauded, not derided. Yeah, they screwed up. But providing them a lower rate way to fix it - and make a buck - is nice...
(Risky business, to be sure, but "nice" if it's done "right".)
Anyway, you're beginning to think about the underlying mechanics, that's good; just be a bit careful with the sweeping generalizations.
This game is much more complicated than just picking one datapoint ("loan purpose") to blame for being stiffed. Ask better questions...
In some ways, lending people money without doing diligence - and then getting mad - is similar to just accepting 'affordable payments'.
So......... there ya go.