I guess I just sort of find it weird that a person can spend $2,000, maybe even $3,000 on a vacation (let alone most who spend 4 or 5 thousand or more) and then cheap out when it comes to a $12 mug.
If Disney's policy was "mug is good for life" then fine. But the rules are "good for the length of your stay." Really, is it up to us as a society to decide what rules we want to follow, regardless of how trivial we may find them, or how much we believe it's not hurting anyone?
Yes, I realize soda is ridiculously cheap for them to produce. But when you start getting into frozen cokes, lemonades, juice, coffee, etc, it can begin to add up. No, Disney won't miss the few dollars they're not going to get, but the bottom line is that if you didn't have the mug, you'd spend the $12 on a new one, most likely, meaning they're not losing the few cents it costs to make each soda, they're losing $12.
And again, it's not really an issue of money. I don't hold anything against anyone who chooses to re-bring their mugs - you make the decision. However, again, my point being is that it surprises me the things people will spend money on at Disney (or just in their lives in general), and then decide they'd rather not get a new mug.
I guess from my perspective there are dozens of ways to save money at WDW, nearly all of which will save you more than the cost of a mug and are things that Disney "approves" of. Bringing your own bottled water and refilling at water fountains, asking for a glass of ice water at a restaurant or coutner service location instead of buying bottled water, bringing your own snacks from home, visiting during the off-season to save money on rooms, etc. So many ways to legitimately save, why should you go up to the drink station feeling guilty every time you refill? Well, anyway, I'd at the very least feel a bit guilty refilling with a mug that I'm technically not supposed to use. The $12 is worth it for a week of not having to feel like someone is going to catch me every time I fill up.