The Michigan Supreme Court found sobriety checkpoints to be a violation of the Fourth Amendment. However, in a split decision, the U.S. Supreme Court reversed the Michigan court. Although acknowledging that such roadblocks violate a fundamental constitutional right, Chief Justice Rehnquist argued that they are necessary in order to reduce drunk driving. That is, he argued that the end justifies the means. Attorney and law professor Lawrence Taylor refers to this as “the DUI exception to the Constitution.”

Dissenting justices emphasized that the Constitution doesn’t provide exceptions. "That stopping every car might make it easier to prevent drunken driving ... is an insufficient justification for abandoning the requirement of individualized suspicion," dissenting Justice Brennan insisted. 2

Chief Justice Rehnquist had argued that violating individual constitutional rights was justified because sobriety roadblocks were effective and necessary. But dissenting Justice Stevens pointed out that "the findings of the trial court, based on an extensive record and affirmed by the Michigan Court of Appeals, indicate that the net effect of sobriety checkpoints on traffic safety is infinitesimal and possibly negative." 3 And even if roadblocks were effective, the fact that they work wouldn’t justify violating individuals’ constitutional rights, justices argued.

Although it's a silly argument to make in public to claim that you'd rather see drivers driving drunk than to submit yourself to a checkpoint search.