Well, they said it was to determine the origins of the universe. But I think your idea is probably closer to the mark.

Sigs by Bob! For the discerning palate!

maybe someone can explain to me why NASA crashed that thing in the first place.
I'm guessing it is because they can, and heck, who doesn't like to blow stuff up.

Astronomer Mike sort of agrees with that last comment (from Discovery):

"Astronomy is a passive science, not experimental," says A'Hearn. "As astronomers, we look. We watch God do the experiments and we see what happens." But the Deep Impact mission is different: "It's a bit of the boy in the sandbox playing, throwing something at something and seeing what happens," A'Hearn says. "The uncertainty of what's going to happen makes the experiment worth doing."

As to why...

We do know that comets are very old and very cold. Some 4.56 billion years ago, when our solar system took shape, the comets formed at a great distance from the sun. Unlike planets, which have been melted and mixed up and remixed and turned over in an endless series of catastrophic processes that all but obliterated knowledge of the beginning composition of the solar system, comets (at least those, like Tempel 1, that are small enough that internally generated heat does not change things) have spent most of their time at a great distance from the sun. There, in a long, deep freeze, their innards have theoretically remained intact.

"Unprocessed ices, ices way below the surface that haven't been warmed and refrozen, that's what we're after," A'Hearn says. "Because they're pristine. That's the ultimate thing we're after."

The question I'd ask is whether it's worth the $279 million, although it's cheaper than sending a human mission or robotic probe that has to return to earth. To put things in perspective, one N.Y. Olympics ($12 billion) would be the equivalent of about 40 of these kind of NASA missions. Alternatively, Iraq war costs for a single day would fund this space mission.

"Timeless at lightspeed."