Not really FL

As you'll note from above, the reasonable suspicion standard (for a search warrant) or the probable cause (for an arrest) and not the the articulable reason standard applies. When a person does not comply, he is simply given a hearing and upon a bench warrant is held in jail until he does comply. Since everything is based on judicial review, should DNA be obtained in an extra judical manner, the rememedy is the court system.

You should also note that as a police officer, it is perfectly legal for me to follow you and pick up a cigarette butt or a used coffee cup that you have thrown away and use it for a sample. I may not come into your home to do this, but I can go through your trash once you have put the can to the curb or thrown it on the ground in public. And believe me when I say that the biggest case in my career (Lyndon LaRouche and his associates) was made through extensive use of that technique. And when I worked sex crimes, some 30% of my cases were solved through just checking the trash.   

As for the reason the Supremes held this way, while I do not have the time to cite case law, I will tell you that these decisions were based on judicial predicate law based on previous holdings, and supprisingly most of the current holdings were done during the Warren Court, which was the most liberal in living memory.