Read these three posts by Virginia Postrel (as this link ages, you may need to scroll down or use Google). This is a difficult topic for me, since I have had dealings with numerous think tanks and think tank-related entities for almost thirty years. I sympathize with much of what Virginia has to say, but here are a few points in the other direction:
1. The existence of think tanks, and related entities, makes being an academic more attractive. I mean the fun and exposure, not the money (think tanks don’t pay so well, relative to consulting). Think tanks can make academics more productive, and can make academics more interested in addressing real world concerns. Such factors have played a considerable role in my life.
2. I am interested in what economists call "rent exhaustion." Why isn’t the entire budget of a think tank taken up by attempts to raise money? Well, the entire budget of a for-profit usually is — or at least should be — taken up by attempts to make money; we call those profits. The true goals of non-profits are more diverse, even when they face budgetary pressures. Even corrupt non-profits do not spend 100 percent of their budget on raising funds. Non-profits of all kinds — including think tanks — introduce a degree of mission freedom that is otherwise not there.
The question depends on what we are comparing think tanks to. The for-profit sector? The NSF? Blogging? Free-lance writing? Direct grants from foundations? They all have their pluses and minuses. The key question is whether the different pieces fit together in a useful way.
3. Some think tanks simply are markers or beacons for the ideologically faithful. I do object to the hypocrisy involved, and to the quality of their policy outputs. That being said, they are providing real services, just as churches do.
4. I view the interaction between blogs (and other decentralized information and opinion sources) and think tanks as a key question for the future. Will blogs "smack down" the rot of lower-quality think tank outputs, thereby leading to intellectual improvements? Or will blogs push think tanks out of serious policy discourse altogether, making them more like churches? Will blogs amplify the influence of some kinds of think tanks, at the expense of others? On these questions, all bets are off.
Note that scholars no longer need think tanks to take their ideas to larger audiences. The think tank sector has yet to absorb the import of this fact. Could Google — and not universities — be the real competitor to policy think tanks?