By and large, I can't disagree with you. But there are a couple of factors that I believe set Disney apart from the timeshare crowd.
First, if a family has established a pattern of visiting WDW annually, prefers to stay onsite, and intends to continue that pattern. I'm sure many families have enough disposable income to make annual cash trips to WDW, but do not have the 15K+ to pay cash for DVC. Even if the interest paid while financing adds another 2-3 years to the breakeven point (say, from 8 years to 11 years), doesn't financing DVC still make more sense than paying cash for the next 20+ years?
Second, resale values are much higher than elsewhere in the industry. No, there is no guarantee that current patterns will continue, but I think it's a reasonable risk to take given DVC's increasing ROFR and demand for rooms at WDW.
We paid $79 per point for our contract at Saratoga Springs. In three weeks we'll be on our third trip on those points. And, resale prices at The Timeshare Store are currently creeping upward of $79 per point. If we had to sell tomorrow, we would still almost certainly come out ahead.