Its rare to find someone who invests in the support characters. I had some amount of care invested into the Miami PD, but ever since the end of S7, it got really stale. La Guerta really stirred the shit and it made you hate her, but she also made it interesting. The stupid previews this whole season have caused us to believe Joey is on to Dexter but it has always turned out to be false... quite unsatisfying. No one in the department has any suspicions of Dexter and that puts a serial killer in a really comfortable spot in a room full of law enforcers. Other than La Guerta, everyone has been totally uninteresting after season 2 (Doakes).
If there is a DEBRA spin-off, I'll probably watch the first show only because I'm a fan of Jennifer Carpenter.
And to relate back to your post, Mokoshne, imo Quinn is a total jack off, but he's not a bad cop. You might have gotten that impression when he supposedly planted the blade on the door handle of Zach's rental car, but that was never confirmed to be Quinn's doing. Yeah he was out for Zach, but I don't believe he killed Cassie to make it look like Zach's MO, I think the BS did that to use as a diversion. Anyway, back to Quinn. Let's just say for argument's sake that Quinn did plant the blade. That is really his only form of acting out as a bad cop, and even when he does do this, his morals get the best of him and we always see him somehow breaking down and admitting to the shit that he gets away with. A show revolving around this would be puke worthy, imo, but it may just not be my cup of tea.
Besides, isn't Dexter our extreme version of bad cop? Except he's not a cop, he's a blood spatter analyst and he doesn't just plant evidence, he kills people... but bad people. Okay maybe he's just undercover vigilante.