I don't remember exactly what it was, but I do know that the investigators determined that there was legal RADAR separation (at least 4 miles in this case).

The biggest issue here is cooperation. I don't have all of the facts about this incident, so I don't know if the controller painted him/herself into a corner or if the pilot was being stubborn, or if it was a little of both. It's fine and dandy to have a CYA attitude, but know that there is a long-term price that may have to be paid. I have known ATCers who held grudges against entire companies due to the actions/attitude of one pilot. If your company has a hub at this airport, then the ramifications can really add up. Fortunately, those folks are in the tiny minority. Most people understand that pilots and controllers are on the same team, i.e. you might save someone's butt today and they might save your's tomorrow. In spite of all of the rules written in black and white, over the years I learned that aviation is just one big shade of gray, and a lot of folks have to put out extra effort to make the system work. If a clearance is unsafe, then by all means refuse it! However, if you just want to be difficult, understand that your actions may have a greater impact than you bargained for.

Visual separation exists in form to "expedite" a procedure in use in the terminal area and enroute airspace system of NAS. There is no requirement for a pilot to "accept" such clearance however in the terminal environment, the ATC local controller can provide this separation if both subject aircraft are kept in sight and instructions applied accordingly. The Heavy Driver was not wrong in declining such clearance but he could have used the word "unable", and everyone here knows what that means. There is too much chatter on the ATC frequencies these days, keeping it short and simple to the point is much more effective.