Blizzard says we do, and it's an old standard of the MMO genre that someone stands up front and annoys the monster into hitting him, so that healing can be concentrated and DPS doesn't have to take a beating that would likely kill it. But do we really need tanks, or should the game move away from emphasis on the tanking/DPS/healing troika?
Everyone in the game can DPS and many choose to: DPS classes seem to be the most popular. We could debate why all day, but at the end whether it's 'big number syndrome' or it comes from a desire to feel more like you're actually hurting the monster than simply poking it with a sharp stick and calling it names (or any other reason) the facts remain clear. Now, removing tanking from the game would mean many, many changes. Healing would have to become much more dynamic and would need the ability to either switch targets more rapidly or more area of effect utility. DPSers would need to be able to take more of a beating, making the cloth DPSers more vulnerable. Raids encounters would in many cases have to be entirely rethought.
As someone who spends about 75% of my time in World of Warcraft tanking, it would be a big change for me. I'm PvPing more and more now than I used to (especially now that there's actual, honest to murgatroyd players standing in my way in AV... I spent an hour in one match today crawling up to that flag over hunter bodies, it felt like) but I still tank and frankly enjoy tanking when I'm with a good group. I don't think I would like to lose that role from the game, even if I do sometimes wish I'd rolled a mage or warlock instead.
Generally my answer to the question is yes. Not only do I personally like tanking, but I think the game has been designed and has evolved around the tanking idea: the paradigm shift would require too much alteration to the game at this point. What do you guys think? Should WoW move away from the three role mindset or should we keep on tanking?