This is a big problem with victimless crimes and offenses against the public welfare. The extent of actual harm to actual people cannot be easily measured, so there is no rational limit upon punishments levied against the offenders.
Evidence that a criminal intentionally acted in such a way as to reduce the potential harms wrought by his crimes is VERY relevant to sentencing, in my opinion. The same holds true for malice and negligence.
For instance, if you sell heroin, that's illegal. If you refused to sell heroin to people younger than 18, and also embargoed and beat the excrement out of anyone you discovered to be passing heroin on to minors, that would still be pretty awful. But it would also show that you were making some attempt to be less awful than you could be. If, perhaps, you kidnapped any customer who lost his job, and forced him to dry out and clean up in your own private rehab, that would still be pretty nasty. But it would also show a commitment to reduction of harm. You should probably get a below-median sentence, as punishments for drug kingpins go.
Contrariwise, if you keep your drug stash and your loaded shotgun in your baby's crib, then screw you, buddy; you're getting the maximum on all counts.