Former Milwaukee D.A. Michael McCann -- who personally prosecuted Dahmer in the '90s -- tells TMZ ... the notion that MPD officers turned a blind eye to Dahmer's victims because of their race or sexual orientation is ludicrous, despite what "Monster: The Jeffrey Dahmer Story" portrays.

The true crime drama is getting a lot of buzz right now, and while McCann says he hasn't seen it yet ... he's aware of how Netflix and co. are playing things -- very anti-cop and leaning into perceived racial and homophobic bias throughout the episodes.

McCann is flatly denying that characterization, saying neither race nor sexual orientation had influenced how police investigated Dahmer. He insists if they'd known they had a serial killer in their midst, they would've moved in immediately to put a stop to it ... regardless of the victims' backgrounds.

He explains Dahmer's M.O. simply didn't allow for them to discover the truth any sooner than they did in 1991 -- when one of his victims escaped and brought cops to Dahmer's apartment.

McCann notes Dahmer didn't leave a lot of obvious evidence lying around, and covered his tracks well.

He also thinks there's something to the fact that Dahmer's victims were men -- saying women who went missing back then were investigated by assuming the worst. On racism and homophobia generally, he acknowledges it's been a problem historically in law enforcement ... but is still adamant that it played no role in how officers went about handling Dahmer.

Of course, not everyone will buy what McCann's selling here ... especially seeing how Glenda Cleveland -- played by Niecy Nash -- alerted Milwaukee PD to Dahmer's behavior many times before he was eventually captured. Many suspect cops wrote her off because she was Black.