Former NYPD Commissioner Ray Kelly on Wednesday attributed the rising murder rates in some U.S. cities to police supposedly acting in a more cautious manner since an officer fatally shot 18-year-old Michael Brown in Ferguson, Missouri, last year.

I think you'll see, you know, the rise in murders in 30 cities, that's the so-called Ferguson effect where cops are less reluctant to engage in proactive policing, said Kelly during an appearance on MSNBC's "Morning Joe." "Certainly that's an issue here in New York."

The idea of a "Ferguson effect" has been the subject of much debate in the past week, following a widely criticized New York Times article that described the theory with what many writers elsewhere felt was an insufficient amount of skepticism .

The Ferguson effect is that police officers -- and to say Ferguson, it obviously involves other high-profile cases, the disastrous events in North Charleston, South Carolina -- but obviously it means that police officers are thinking twice before they engage, Kelly said Wednesday. And with the advent of cameras, which I ultimately support, but cameras are going to make police officers hesitate somewhat. In some people's minds, that's good. In some people's minds, that's bad.

Kelly, whose book Vigilance: My Life Serving America and Protecting its Empire City was released this week, claimed that because of the heightened scrutiny of police officers in the past several months, cops have become reluctant to do what has been done in the last 20 years.

He also defended the NYPDs controversial stop-and-frisk policy -- a tactic he says is meant to prevent crime and to arrest people ultimately or stop them from conducting their suspicious activity.

If you look at how it's written, it says that if someone is abroad in a public place, a police officer sees suspicious activity and he suspects that crime is about to happen, is happening or has happened, he can intervene, Kelly said. So obviously, it's meant to prevent crime and to arrest people ultimately or stop them from conducting their suspicious activity.

The former commissioner noted that Bill de Blasio was an outspoken opponent of stop and frisk during his mayoral campaign in 2013 -- a year when, according to Kelly, the NYPD had a 70 percent approval rating. That was also the year U.S. District Court Judge Shira Scheindlin ruled stop and frisk unconstitutional, concluding that it violated civilians' Fourth and 14th Amendment rights.

"In practice the policy encourages the targeting of young black and Hispanic men based on their prevalence in local crime complaints," Scheindlin wrote at the time. "This is a form of racial profiling."

NYPD Commissioner Bill Bratton admitted in June that his stop, question and frisk policy was partly responsible for the rising arrest rates among African-Americans and Latinos.

Morning Joe host Mika Brzezinski pointed out on Wednesday that only a tiny percentage of the people who have ever been stopped under the NYPD's policy were actually carrying guns. Co-host Joe Scarborough argued that this is proof of the policy's effectiveness.

If you know that you're going to be stopped by police officers, you're going to be less likely to carry guns, he said. If you're less likely to carry guns, the streets will be safer."

That's one way of looking at it, or you can look at it as a lot of innocent people are getting shaken down and that it's unconstitutional, Brzezinski responded. There's two ways to look at it. That's the controversy.

Kelly's comments on Wednesday echoed an argument that's become common in the past year -- that when law enforcement officers are afraid to do their jobs, it results in dead cops, not safer streets. But it's not hard to understand the counterargument that it's perhaps not the worst thing in the world if police don't automatically resort to lethal force every single time. As The Huffington Posts Nick Wing recently pointed out :

It won't be long before an officer somewhere will draw his firearm on a "criminal" who isn't a criminal at all. And in that situation, the officer's choice not to shoot will have drastically different implications. Perhaps, like [homeless man James] Boyd, he will be someone who prosecutors say should still be alive. Or maybe, like Tamir Rice , he will be the 12-year-old boy who doesn't get killed for playing with a toy gun at a park. For all the hand-wringing about hesitation, it's worth remembering that the lack of hesitation has led to its fair share of tragedies, too.