NASA's next small step: to an asteroid

Some time ago, I caught wind of an idea I really liked: instead of our next space destination being the Moon (again) or Mars, we should go to a near-Earth asteroid. I loved this idea. It has a lot of merit: a lot of these rocks pass us at relatively low speeds, making them easier to get to in terms of time and fuel. We know very little about them, and a manned mission will teach us a lot about them (as well as how to do long-term missions like this). And given that these objects can be a real threat, the more we know, the better. I was interviewed about this briefly for an article in the Houston Chronicle where I give this opinion. The article has some interesting info about a potential asteroid mission, and I really do think this is a good idea... except for one thing. ...