timv: the OP is warning people to avoid talking to cops. "Most cops are good" is a very common sentiment that is even inculcated in kids growing up attending public schools. This widespread common belief contributes to people speaking naively to police and thereby getting themselves in trouble. That is what I meant by dangerous. I didn't explain this in my reply to mikeash because it seemed to me that mikeash was being obtuse given the context of the OP.
The good cop:bad cop ratio is utterly orthogonal to whether or not it's a terrible idea to talk to them without a lawyer present. They still have to do their jobs, and if you say something in the course of speaking with them that furthers their investigation, directly or indirectly, they're kinda obligated to pursue it.
Even if they're the nicest person you've ever met.
Edit in reply to rosser: I agree with you there.