actually it would make a certain amount of common sence to not codify this technology. The sorta "catch 22" is that, the more commonplace the use of this sort of "fingerprinting", and the more common the knowledge of this possibility, the more likely the fingerprint will be tampered with before a crime.
I agree that there shouldn't be reason to resist this -- except maybe as weighing cost against effectiveness. Still, there is also no reason, other than an election and a tragic event that has the national attention, that has this (ballistic fingerprinting) being brought to the public attention.
This has been brought up to try to make a political debate out of the Beltway sniper -- and it is a complete non-sequitor. It wouldn't help now and it wouldn't help if it had been in place -- if the guy's smart enough to evade the law to this point, he'd also be smart enough to change the "ballistic fingerprint" of his weapon(s).
Doesn't stop politicians from trying to make points with it though while we're in a frenzy. Damn the facts.