I'm a little leery of using the term 'entitled' here. We don't really know how many people are walking around saying 'I deserve a 17th level spell-caster who can totally break open this game and make it unfun for someone trying to play a fighter.' What we know we have is forumers saying 'y'know, there's some really high-powered stuff here that kinda breaks the game open.'
Look what he was responding to, though--the comment that just playing the game at a lower level isn't the answer. I probably wouldn't have used the word "entitled" but he nailed the general idea. Just because higher levels were included in the game doesn't mean they have to get played. I saw this mentality creep in with a lot of 2nd Ed campaigns as well, you might recall attribute scores up to 25 were included in the players handbook. There suddenly seemed to be a lot more reasons to have scores in the 20's, not the last of which was Dark Sun where the character generation method allowed scores of 20 before things like racial modifiers were applied.
So here are the choices.
1) You can keep the game as is, where the high power stuff is printed, but yeah, you're not really supposed to touch it much.
2) You can just remove that content from the game or at least the PHB, kind of like how the 1st Ed PHB didn't show stats above 18 (even though it is possible BTB to have higher scores).
3) You can keep things as is and just suck it up, realizing that 1st Ed had stats for gods, that at 12th-14th level PCs are approaching demi-god level, and recognize it's not the power level that's broken but rather your expectations, and shift those expectations to running a game for demi-gods, or
4) The Spinal Tap solution, where you are basically doing #2, restricting MU's to about level 10 or so, but then are just calling it '11' (or '20' or whatever level you think the game ought to go up to).
I just don't see how something like #1 or #2 is "not the answer" but #4 is.
Though I did find the mandatory multi-classing an interesting idea. Mainly because, in non-mandatory form, it's always the answer I gave to people who bitched about 1st Ed level limits for demi-humans. Don't like them? Multi-class as a thief. You'll still improve beyond your max level in the other class, it would just be a slow rate of power gain... which is what a lot of DMs back then house-ruled anyway, allowing level progression to continue, just requiring double (or more) normal XP.