Answering the question of whether there is systemic racism in US police departments requires two steps. First, you must define racism in this context. Does mere stereotypical thinking about people of another race suffice? Or is animus or hatred required? 

The second step is to investigate and analyze the facts. There are roughly 800,000 police officers in the United States. Some portion of them are racist. And a thorough analysis of the relevant facts (including disciplinary records, academic studies, whistleblower reports and litigation dockets) will yield insights about the percentage of cops who are racist.

Instead of performing this rudimentary and necessary analysis, however, most commentators do little more than hurl ill-defined and conclusory assertions in competing directions.

Police brutality is widespread. Police brutality is rare.

There is systemic racism in police departments. There is not systemic racism in police departments.

Black lives matter. Blue lives matter.

And so on.

It's time for people to start showing their work. The extent of police racism is an empirical question. Assertions should have facts -- and not simply cherry-picked data -- backing them up.

Moreover, an important part of determining the percentage of police who are racist is eliminating extreme positions that are self-evidently false.

Everyone should acknowledge that our nation has a profound and deeply troubling history with racism. Slavery was embedded into our founding document and survived for a century. It took a civil war to end it. And Jim Crow followed. The outrage in response to police brutality must be looked at in this historical context. And both sides should acknowledge that at least some police are no doubt racist -- under any definition.

Likewise, everyone should acknowledge that there has been some progress with police departments over the decades. Current American police are not the Jim Crow police. There are more laws protecting people from the police than there used to be. And meaningful reforms have occurred. While we have a long way to go, we have come a long way. And both sides should acknowledge the simple proposition that many police officers are not racist.

The question of how racist the American police are is a factual one. The answer does not reside in the subjective mind of any individual, no matter how loud she or he screams. It lies in the empirical world, somewhere in between the extreme (yet commonplace) assertions from each side.

This important debate would be enriched by acknowledging this, by defining racism, and by sorting out the facts. As in other contexts, unsupported conclusory assertions ring hollow and therefore only harden the entrenched views of each side.

The facts matter, too.

William Cooper is an attorney and columnist who has written for The Wall Street Journal, Baltimore Sun, New York Daily News, St. Louis Post-Dispatch and USA Today, among others.