Rage is a broken mechanic.
It's broken in that it allows DPS warriors (well, okay, fury warriors) to do DPS almost equivalent to that of "pure" DPS classes, if the warriors are wearing the absolutely perfectly ideal gear setup and are in an encounter that is absolutely, perfectly suited to them (i.e., one that allows for a lot of Heroic Strike and Cleave spamming with minimal lost time that keeps rage generation down). It's also broken in that it constricts lesser-geared warriors to doing a fraction of equivalent hybrid-class DPS.
Rage is broken in that it starts at zero, forcing a warrior to either take damage or deal white damage to generate rage or use an ability like Bloodrage, while other classes start with some or all of their resources and can open up with a powerful ability to start. This makes it far harder for warrior tanks to generate snap aggro and keeps warriors from having any sort of a rotation, forcing them to rely on priority systems instead. Both tanking and DPS warriors tend to find themselves spamming abilities to generate threat/damage, with one of the biggest culprits being Heroic Strike.
Furthermore, the warrior DPS spec that uses HS the least is at once considered overpowered in PvP due to its use of rage as a resource (at least, "overpowered" in that sense where everyone attacks you first and kills you in the first five seconds if possible, so you end up not really doing much of anything unless someone else keeps you alive via heals/peels). This spec finds itself benefitting the least from gear scaling that allows other warriors to gain exponential increase in their DPS.
Don't believe me? Let's see what Ghostcrawler has to say.
The problem is simple. The hybrid tax? It applies more to undergeared warriors than to any other hybrid. A warrior who is poorly geared hits less often for less damage and generates less rage, therefore having less rage to use for special attacks and hitting even less hard. Likewise, the better a warrior's gear gets ... the less he or she is dodged, the less he or she misses, and the harder his or her white hits are, the more rage he or she generates. The more rage for specials, the more often he or she can use them, can queue up Heroic Strike and can hit Bloodthirst, Whirlwind and instant Slams from Bloodsurge. The better the gear, the harder all of those hit, as well. So the issue isn't that warriors don't pay the hybrid tax. The issue is, they pay it more and harder to start, they have to eat lower DPS and lower ability to perform and they have to be carried by raids and given gear that was achieved despite their presence, not because of it. Once they manage to get through all of that and have finally arrived at the best gear they can possibly get, then their damage ramps up because of the exponential nature of their resource management and the means to gain it. Hit harder and more often, get more rage, use rage for specials, specials hit harder and more often.
Burn it or it's wasted
Rage has been normalized before, of course. It gutted the class for months. I've never gotten over the ham-fisted, overly aggressive way rage was normalized when BC shipped. The problem with rage and rage normalization is now what it has always been: when you rely on rage, you're basically fighting the game itself to gain the means by which you play it. Mana classes gain more mana as they gain better gear. They can gear for mana regen that can keep them in a fight longer, but their spells cost a fixed amount of mana, so as their mana pools increase, they can do more things. A rage user doesn't ever get a larger rage pool. There are no runes or combo points to manage. Rage itself is both resource and resource acquisition. So as warriors gain more power to damage, they gain a faster and faster return mechanism -- but the ceiling on their resource remains the same, rewarding a frenetic, "burn it now or it's wasted" style of play. There's no reason and no reward to having max rage.
Another difference between rage and almost all other mechanics of mana/energy/runic power is that rage is the only system that returns resources both when you do something (damage an enemy) and when something is done to you (you are damaged). So in fights with environmental damage that can't be avoided, warriors suddenly have far greater return on their investment of resources than any other class, through no fault or good decision of their own.
I'll use some examples to illustrate. I have two level 80 warriors running heroic dungeons. One is in a mix of Naxx-25 to heroic Halls of Reflection gear, iLevel 213 to 232. The other is in heroic Trial of the Crusader through hard mode ICC gear, between iLevel 258 to 277. The first, my tauren, can average around 4k DPS in a heroic, more on a run with lots of trash like Halls of Stone. The second, my draenei, can easily push 8 to 9k DPS in the same instance. The tauren is expertise- and hit-capped for heroics, but my draenei had more attack power (nearly 1,000 more, in fact), much more ArP (he's nearly hardcapped), and more crit, plus higher weapon DPS. Alone, none of these would contribute to more than double the DPS of the (still fairly well-geared) tauren. The tauren's 2H axes still have about 232 DPS, as compared to the draenei's 294. By itself, that 62 DPS difference wouldn't make up 4.5k or so. But on a warrior, each gear upgrade acts as a multiplier, and in addition, warrior DPS is actually rewarded by playing chicken with environmental damage and your healer's skill and mana. The more damage you can connive to take and survive, the more damage you can do.
A broken mechanic
Rage is a broken mechanic. It punishes the leveling warrior and the poorly geared warrior. Of course, no one from another class cares. They see their own DPS trumping the warrior's and see it as their own skill and ability. Rage rewards the foolhardy and supremely geared warrior, and of course everyone else sees this as warriors' having an unfair advantage. It causes tanks to spam abilities because there's no reason not to ... Rage starvation is a nonissue for the endgame tank while being a major concern for those who overgear content, putting tanking warriors in the unlovely position of wearing DPS gear (or no gear at all) to ensure its presence.
Rage should be and will be overhauled in Cataclysm. And if/when they get it wrong, they will absolutely hobble the class. My own personal hope is that they do something to make the way rage interacts with each stance unique, building on the way they made arms warriors prefer battle stance, to match fury staying in 'zerk and protection relying on defensive. If tanking warriors use rage differently than DPS warriors, you can really start to make changes to rage without crushing the class' potential for months. Rage is a broken mechanic, yes, but it's deeply unfair that the only time it's ever 'fixed' is when its overperforms, and never when warriors are struggling to solo and level and run instances in starter gear.