For me the people complaining about the rise in the level cap generally fall into a few different categories.
First, there are the people who don't like leveling. They embrace the idea of new content, they just find leveling to be a painful grind that interferes with their enjoyment of the game. For these people, I have a measure of sympathy. There are a lot of jobs I never particularly enjoyed leveling, and I'm not looking forward to the idea of going back and leveling them again. Lots of subs, lots of levels needed for those subs, lots of time spend in E.Ronfaure killing Colibri. Too much of that makes Raes go something... something...
Second, there are the people who just fear change. They don't trust SE to do the job properly, they're worried about the complications that will arise when the range of abilities granted by subjobs expands enormously, and they are equally concerned about the amount of content that SE can possibly provide for this sudden and profound of a change. As before, I have sympathy for these people. It is a very abrupt alteration to a game that has remained essentially stagnant for almost its entire lifespan. I like to think that a lot of the little things SE has been throwing at us over the past couple years (augment, evolith, level sync, etc) have been preparatory measures for this coming expansion, but there's no way of knowing for sure until the process actually begins.
Finally, there are the people who have gotten their jobs to 75, geared them to their liking, and are royally pissed off that SE is going to make them get new gear. Most of the people who fall into this category that I've talked to are upset not because there will be new gear, new challenges, and they're just burned out from having achieved all that they have. For that sub-group, I have sympathy. But no. Most of them are upset because other people will be able to get "better" gear without the same effort. It's analogous to the bitchfest that occurred when SE made the Thief's Knife a trivial acquisition.
Bear in mind that we have no idea what kind of gear is going to be offered to level 75+ characters, and the inclusion of the Trial of the Magian system tends to lead one to the conclusion that they're not going to be making cheap equivalents of your Ares Cuirass, Adaman Hauberk, or Ridill. But that's largely irrelevant to the knee-jerk "I'm-gonna-quit-SE-sucks" crowd who are just pissed off because they feel that their e-peen will get proportionately smaller.
For those people, I have only a hearty laugh at their expense.