The Supreme Court could have declared that the search can only be for evidence of a particular nature for which the police already have probable cause and that failure to yield to a pedestrian is not probable cause for drug possession (of course, if we're just evaluating things on epistemological grounds, failure to yield to a pedestrian is not a probable indication of anything interesting).
Nothing in the judicial system supports that at the moment. Reason for action is considered immaterial for fourth amendment purposes across the board.
I was going to point out an example of the complexity of this, but someone else pointed out that the right of cops to search an impounded vehicles is an interesting one.
