Most cops are NRA supporters. It's just that ones who aren't get the ink.
Twenty years ago, I'd have agreed with you 100%. Unfortunately, today those cops are all standing in the line to retire! Todays cops are (think about this) mostly all products of the public school system. Our soldiers, too. That corrupt system Of EDJAMACATION (I've been a high school teacher for sixteen years, I know) has been infested by the liberals since the 1960's and getting worse every year. The public schools universally push one agenda: GUNS ARE EVIL and anybody who either owns or wants to own a gun must be evil as well! The terrible by-product of this is that the protectors of society are incompetent gun handlers and they have attitudes that are so PC that they'll get killed in many standard tactical situations.
The proof is in the firing range qualification standards and the incontrovertible fact that most cops cannot shoot. The exceptions being of course SWAT, narcotics and special squads like warrants and gangs. Sidearm qualifications have been changed over the years to PASS/FAIL rather than scores. Why? Because the departments all know how terrible their guys are at shooting and that even good training can't overcome the brainwashing that's taken place over a 12-16 year period. A terrible shot that is a police officer is just one long line of lawsuits waiting to form with every miss and subsequent strike of an innocent bystander. The shoot qualification scores are going to be plaintiffs exhibit #1.
Tactics and armament have changed as well. Like the difference between the US Army and the USMC where excellent skill at arms is mandatory versus the spray and pray mentality of the army. Cops have been switching to the high capacity 9mm for decades. Why? Less recoil and greater magazine capacity. Spray and Pray all over again. Used to be six rounds of .357 medicine solved nearly all problems unless you missed. Well, out of 15 rds of 9mm, about 90% are misses these days. Sometimes, even 9mm hits can be disregarded until hydraulic loss (bleed out and expiration of life signs) takes effect, because dynamic hits are not being achieved by the shooter with a badge.