Well, Coyne, one thing that it would do would be if someone stuck a flyer under a car's windshield wiper, and the flyer offered illegal services, secondary liability would make the driver of the car guilty of offering the illegal services too.
I'm diabetic. I routinely have syringes and vials full of liquid (insulin) on me, especially when on trips lasting multiple days. I also work in IT, and I have a syringe very similar to yours in my toolkit.
Insulin has an odd side effect on me -- frequent insomnia. When I go over 24 hours without sleep, I get glassy eyed.
I don't smoke, I don't drink alcohol, and the strongest drug I've ever self-administered is Tylenol. But going by physical appearances and what you'd find in my backpack, I MUST be a drug addict!
If the only possible use for scales was weighing drugs, then your point would be valid.
But that's not the only possible use. It's not even the majority of the uses scales are put to. Possession of a scale isn't illegal in itself either.
Therefore possession of a scale proves absolutely nothing other than the person possesses a scale.
Some people have bad skin. Some people get drunk and ride as passengers because DUI is illegal. Glassy eyes can be caused by any number of things, including tricks of the light -- I myself get glassy eyed when I've gone more than 24 hours without sleep, and I've never taken anything stronger than Tylenol in my life (full disclosure: I had surgery once that involved general anesthesia, but I didn't apply it myself).
The totality of the circumstances added up to the fact that there was no probable cause to search or arrest the passenger.
Police apologists regularly proclaim that because a police officer was 'baited' or 'provoked' into abusing his authority and/or breaking the law, he should be excused for it. But the thing is, police departments engage in sting operations every day, where they go a lot further than amateur photographers to bait people into committing a crime in their presence.
If 'baiting' someone by giving them an opportunity to choose to obey the law or to choose to break is invalidates the results of making that choice, then there are an awful lot of wrongfully arrested and wrongfully convicted 'victims' of sting operations behind bars.
Instead of impeachment, how about adding a clause to the definition of treason, to include willfully and reasonably knowingly acting to subvert the constitution through legislative acts other than the well established process of amending the constitution?
The more education you have in the law, the more that clause would bite you for introducing unconstitutional bills. Treason is a crime you can be impeached for, so it handles your idea as well.