That's not true; it doesn't make sense to me even if it were possible to guarantee proper handling. The risk of the government abusing it's power in a completely legal way is greater than some crimes going unsolved because documents remain secret.
What matters to me is the power imbalance; with few exceptions whatever the government can do, normal people should be able to do to.
The 4th amendment doesn't mean you can do every illegal thing in the world and never fear the state...simply the state cannot engage in fishing expeditions. If 5 kids are reported missing from your neighborhood, and a day later you have a backhoe digging on your backyard, be ready to answer a few questions--that may lead to other questions and warrants.
>>The risk of the government abusing it's power in a completely legal way
No such thing in a western /democratic society. After you go all the levels, you must obey. Sometimes it sucks, but...