This sounds grossly harsh, but I refuse to read stories where the LI is a crime boss, in the mafia, etc. It doesn’t really matter how you frame them or if you avoid making them a hero. They are dangerous people and are murderers. Once you’re in the mafia, it’s impossible to leave… so even a plot centered and that is unrealistic.
What I would want in a mafia or crime story, would be to see detectives TAKE. THEM. DOWN. Maybe the the two detectives could fall in love with each other while working together? Stories with detective work are interesting and can be very interactive; I love them. Plus, this type of plot avoids any sort of accidental romanticization.
IDK, it all just goes back to my first statement: I will not read a story where the MC or the LI is involved with crime and / or the mafia. Too many people have been affected by the mafia and organized crime for me to even think about entertaining the idea of a story that treats the mafia as anything other than an abomination in need of destroying.