You are ignoring decades of economic precedent here. Consumers do not delay gratification. From phones to cars to clothes to homes, people will buy shit they can't afford for the experience of having it now. Drawing the line in the sand for videogames seems arbitrary and weird.
I never said people won't do it. They will. They'll flock to it in droves, I'm sure. It's a smart decision for MS because it plays on exactly the kind of human weakness you suggest. That in no way makes it a good deal or a smart decision for consumers. I only said there is no economic argument in which this makes sense for consumers. Hence, "Maybe you have $500 but I don't..." is not a sensical argument, because you'll be paying more than $500 in the long run. "I need to have this luxury item NOW," is not an economic argument, but an emotional trigger.
I draw no line here either. This doesn't just go for video games, but for anything being sold with such a plan. The only places where it makes sense are where attaining such a high degree of liquid funds would be unrealistic, or where you can't afford to delay the gratification. Cars and homes would be examples where it does make sense to have a payment plan, but even there, people need to choose the options that are within their means.
And this is especially true during the holiday season.
Even more so than before, you're talking about an emotional argument, not an economic one. That $300 price tag will certainly seem more appealing that a $500 one at Christmas, but that in no way makes it a better deal in the long run.
That's a very ignorant statement. It's all relative. Just because you can afford to spend $500 dollars on a console doesn't mean that everyone can.
But you ARE PAYING $500 for the console, and more. You're just spreading the pain over a longer period of time, and ending up with more pain in the end as a result. If you're buying the console, you do have the $500 to pay for it. You might not have it right this minute, but all you have to do is save the money you'd otherwise be spending on that subscription until you reach the $500, and you'll end up saving money. EVERYONE can do that.
The only world in which this makes sense is if you have a fixed monthly income that you lose if you don't spend it. The programs I can imagine which use such a system are one's where you wouldn't be in any position to spend your money on a new Xbox.