I'm afraid that for younger cohorts of our citizenry the term "predisposition" is, largely, just another fancy word. For others of us, the connection to the erosion of Fourth Amendment rights/protections is only all too apparent. Much more subtle, however, is the impact that this portion of Drug War Jurisprudence has had in helping to create limitations upon even Freedom of Speech.
Literally, and probably unbelievably for those who missed a certain very small time window that closed sometime between the early and late sixties, the possibility of there even being much of "A War on Drugs" seemed reasonably remote. Established law, itself, stood as a barrier to effective law enforcement in this area. Taken literally, at least in jurisdictions which afforded the strongest protections to personal liberty, police were simply not able to make drug busts where there was reliance upon transactions in which either an undercover officer, or even a "cooperating individual" (snitch) participated.
To inject law enforcement activity to deeply into persons private lives was seen as being impermissible. Drug busts would be made, Supression Motions would be filed, and cases would die upon a finding of entrapment. A Fourth Amendment violation, that. The operative language of the 4th has always been the phrase "unreasonable searches and seizures" and U.S. society had generally thought it not "reasonable" for police to be sneaking around to the point where they were clandestinly inserting themselves into participation in criminal activity. Incredibly, Americans once very much more sincerely than now believed that law enforcement personnel were obligated to live law abiding lives.
Not terribly expedient, but there you are!
Or, were, if even only very briefly. Because, if you want to get right down to it that was not only a "loophole", but a crippling one, and any attorney who was any good at all needed only about ten seconds to argue that "laws are designed to protect society, not criminals". Then someone slapped the label of "Predisposition" onto this self evident principle and our age of innocense pretty much ended entirely. "Avoid entrapment" became something very much closer to "go get the bastards (and an extremely open ended category that), and let it be by hook or crook". So, in an incredibly short evolutionary period we were fully engaged in the supremely important "war" to save good, decent, law abiding folks from the dirty hippies.
But then we get to where The Fourth Amendment morphs into The First Amendment, because, to prosecutors and judges, "predisposition" is like "porongraphy", they know it when they see it. Have a copy of High Times in the house? Write about legalization on a blog? Or, even better yet, write or say legal things about favoring Jihad, and you have just declared open season on yourself.
Well, I'll leave it up to others to discuss the impact of all of these merging currents, but my travels through life and the legal system have left me with the clear conviction that some of this stuff snuck up on us in ways that many people might not have noticed happening. And, yeah, there's a lot of simplification here, but sometimes The Readers Digest version (for those old enough to remember TRD) works to get a message across.