So Uni crossed that line as well (some years ago, I suspect) with the HHN add on express passes, RIP Tours and such?
The "wrong" thing about upcharges for me is when they take away from what would/should be available to those not paying the upcharge. Allowing pay for express pass/fastpass/flash pass is, IMHO, the worst cash grab there is. And Uni and Six Flags and Cedar Fair and everybody else does it but Disney. I hope Disney doesn't start, and think that we'd bash the heck out of 'em if they did. But the others don't get held to that standard.
As a parkgoer, I want Disney to make the best use of the park assets they can without hurting the experience of the plain ole guest. Wild Africa Trek, the early morning safaris, backstage tours, late night Epcot wind-down, hard ticket events when the park would otherwise be closed, Harambe Nights, special food events, and evening EMH (extending beyond normal closing time) all pose no concerns for me.
Morning EMH I don't like much because it screws up the lines for "regular" guests. And allowing people to pay for prime viewing locations that would otherwise be available to regular guests -- I don't like either.
But the mere fact that an already hard ticket event has upgrades possible doesn't bug me. Until they take away from what would/should otherwise be available to regular hard ticket event people. Of course, determining what would/should be available is a judgment at times, but it's pretty easy when it's something that was available in the past, and is being taken away this year.