Absolutely. Parking is charged where tons of people want to get into a relatively small space (i.e., sporting events, concerts, etc.). The farther out you go, the cheaper the parking gets until it's free again. WDW already charges for parking right next to their parks.
Why are day guests allowed in for free if this is to mitigate the desire for parking? You can't answer that question because it's not the reason for charging a parking fee. Those other hotels that charge for parking are usually right next to something requiring their charge (convention center, arena, etc.). And they wouldn't be letting day guests park for free (maybe a reduced charge).
Other venues charge for those not on official business at that location (thus, validated parking). What's more legitimate than staying at the resort?
Ever been to the All Stars? They aren't exactly touching a park. Nobody's clamoring to park there. And we were already paying for parking in the resort overhead. It just wasn't itemized.
WDW boasts 40+ square miles of space. And don't forget they already charge above and beyond rates at lodging nearby (with continually diminishing perks). The problem here is that they are charging for something we were already paying (rolled in), and they also boosted the cost of that twice in the last year. Once just last month. Why is the Contemporary so much? Because it's right next to MK. The cost has been baked in forever, until now.
I disagree, fundamentally, that it's nothing to get upset over. And I think quite a few people agree. You don't, that's OK, but others are passing their breaking point on the nickels and dimes.