This isn't just an abstract matter. When police are able to act with impunity, it leads to bad policing, bad behavior, bad justice and a bad society.
The process of requiring police to have reasonable cause, and enforcing that standard vigorously (as has been regrettably deeply downplayed in the United States), forces police to do their job. It guarantees that they spend less time with false positives (and false negatives).
Decades of research show that police are far more likely to exercise their biases when they have free reign. Forcing them to behave by certain transparent standards not only builds trust between communities and police (without which law enforcement is virtually impossible), but also makes sure that they act in a manner that will respect the diversity of communities. Given the scale of the problem of racial inequity in the present American criminal justice system, the risk of biases of any kind disrupting fair procedures should be given substantial weight.
Allowing police to pull a driver over without cause empowers police to shake down drivers, behave abusively, and misuse their position.
The rights of people to be able to get to work, play, school, vacation destinations and to be with their families with a reasonable expectation of being unmolested is vital to a society worth living in.