I agree that going on
Disney Vacations is a luxury purchase. No doubt about it. You can debate with folks about whether such luxury purchase is a "good use" of their money, but that debate is never going to go anywhere. It's like debating with a corvette owner about why they would purchase such a limited use vehicle over a minivan or work truck.
My point was that if you've already emotionally committed to consistently making that luxury purchase,
DVC can be a rational slam dunk as long as you do it right. So, it's really not a DVC versus non-DVC argument that most people want to have. It's a Disney versus non-Disney argument. And, like politics, you're never going to be able to change someone's set-in-stone views on it, so why try? I'll never understand people - like in OPs experience - who do try. But, I always try to reframe the DVC question in that way because I think it's the crux of what they're wanting to debate.
Your points are well-taken in some cases. I think my experience may just be different. In my case, I could sell my contract right now at a gain, so I expect to get most or all (or more) of my initial investment back because I won't hold my contract until expiration. So I don't amortize the cost of my points into my annual cost. But I get why others who have a different outlook would. I view my upfront investment as just lost opportunity cost right now, which, to your point, is probably somewhere in the $7 pp range, conservatively.
It's getting hard to find good rentals at $18 pp anymore (happy to take some VGC or VGF points off ANYONE'S hands at that price, haha). Most have moved to the $19-21 pp range even for SAPs. And that's through a direct rental, like the threads on this page, which most ordinary folks aren't aware of. Go onto the public Facebook sites (actually, don't, they'll frustrate the heck out of you because it seems like EVERYONE has a sob story about how heartbroken they are to have to sell their points, for the first time ever, for $26 pp -- I truly feel for those people, it must have really been devastating circumstances that led to them taking such a haircut). Or, even the site sponsor's and their competitor named Dave's pages -- rentals are at about $25-26 pp. And then renting has its own lost opportunity cost. For most private rentals, you have to lock up a few thousand dollars for up to 11 months if you want to do it right, so even the $18-20 pp private rental can't really be priced at face.
So yeah, maybe it's just my own situation that I'm speaking from, but, for us, DVC has been financially a very rational decision. I'm in finance, I wouldn't have bought it otherwise haha.