I bet this person is a lot of fun at parties too!
Nevertheless, I do think you need to look at DVC from the financial perspective, and this is how I respond to this type of person (granted, I'm a bit more analytical):
A non-DVCer COULD still go to Disney every year and stay at Deluxe resorts and have the same experience as a DVC member. If money was literally no object, your Disney experience as a non-DVC member versus a DVC member would not be materially different. So, the question about whether to purchase DVC is really just a financial one, not at all an emotional one. But, unless you have access to ROIs that most ordinary folks do not, if your future plans involve Disney parks*, it's a pretty slam dunk case in favor of DVC. At many of the resorts, you are giving up the time value of your cash (maybe an 8% annualized ROI, or so) for deep immediate savings. My points cost me about $9 per year. A non-DVCer would pay about $26 to rent them through a reputable broker. To pay the cash rates, it's the equivalent of $30-$40+ per point in many cases. So yes, I am trading the time value of my cash to save thousands of dollars on something that I was already going to purchase. The key assumption being that I was already going to purchase this; you need to accept that fact when doing your comparative analysis.
What's my alternative, then? Not buying my DVC membership and investing the cash. Let's say I bought 200 points resale at $150/per point. That's a $30,000 investment that I'll probably recover when I'm done, potentially even at a gain. Let's say I use my points consistently every year, and that the cash-rate equivlent of my points is $30 (which is really conservative). Given that my dues are in the $9 range, that means I'm saving at least $21 per point, or a total of at least $4,200. I could not expect to realize $4,200 in earnings every year by investing that $30,000 in the stock market. So, my DVC membership puts me in a better financial position than paying cash for my room.
* With that said, the true debate this person wants to have is actually whether or not purchasing a Disney vacation - DVC aside - is a good use of your money. But that's a subjective question that everyone is going to answer differently and one for which there is no right or wrong answer. That's also probably not a debate that's worthwhile to have AT WDW.