Elliot Stabler feels what he feels when he feels it. Often, in the interrogation room with one of these criminals, what he feels is blind hot rage. During a department mandated psychiatric evaluation in Season 1, Episode 22, Stabler actually admitted to fantasies of murdering the pedophiles he’s tasked with apprehending. (That’s probably not the time or place, but you do you El.)
His tactics have been called into question on more than one occasion (like a lot), getting him suspended or visits to the department psychologist. For the most part, he plays by the rules, but there have been plenty of times where his aggression has gotten the better of him. We the audience always know when it’s coming. When Stabler gets quiet and starts to unbutton and then roll up his sleeves, things are about to get real. He has slapped, throat chopped, headlocked, and snatched up many a “perp” in order to get his point across.
Now, his interrogation tactics aren’t always physical. Stabler has a way of playing smooth mind games with these sex offenders as well, making them believe he is actually on their side. But mind games aren’t really illegal, are they? One could argue that every time Stabler roughed up any one of these criminals, it counts as police misconduct. However, paperwork and internal investigations don’t make for good TV does it?