A recent writer questioning the logic of announcing planned traffic checkpoints, correctly presumed "some law" was the reason for this advance warning. That law is the 4th Amendment to the U.S. Constitution.
While I sympathize with the writer's frustration (this presumes criminals read the newspaper) we in the U.S. enjoy the right not to have our "person, places or things" randomly searched without a warrant signed by a judge. This warrant, a sworn affidavit, acts to hold someone accountable for unreasonable searches. Without it, law officers could, for example, set up a "neighborhood checkpoint" and search all houses on a particular street without notice or warrant to possibly catch someone doing something illegal.
While the straw man argument "If one has nothing to hide why not let them search?" is frequently espoused, how many of us would really stand for unwarranted searches of our homes?
Our Founding Fathers believed the right to be secure in one's own home was critical; it was an essential one of the Bill of Rights demanded by our representatives.
Providing lawyers to criminals can similarly be seen as helping avoid jail, yet we provide a right to counsel. Or, as in the case of free speech, we must accept hearing that we find abhorrent and would fight a lifetime against, but willingly protect the right of the speaker to say it. These are some of the sacrifices necessary in a free society.
Wheras the Constitution can be amended, I believe the Founding Fathers got this one right.