I believe a more correct telling of the tell is persons refusing to give a sample will result in law enforcement obtaining a search warrant for the person's blood.
By accepting a driver license in most states you give implied conset to give a breath or blood sample upon request of a law enforcement officer during an investigation of DWI/DUI.
DWI/DUI is one of the hardest criminal offenses to prove in court. All the alleged defendant has to do during a police investigation is refuse to perform standardized field sobriety tests and refuse to a a breath/blood sample. This pretty much prevents most evidence of the crime from being used against them and forces the police to obtain a search warrant for blood. During this time, the defendant's body is eliminated the alcohol in his blood, literally destroying evidence.
In addition, the Kansas City Study showed that the level of visible presence of police in a community has no effect on the level of crimes committed. More or less marked cars. More or less uniformed officers. No change in the level of crime.