Well, I'll throw in my .02 in here. First off, I don't believe in any type of "purist" type of fishing. Is flyfishing, or any other the all mighty method of fishing. HELL NO!!!!! There are no elitist methods nor is one man's version of fishing better then another, just different in my opinion. Except, I do believe that being a snagger isn't fishing. I see it as just reefing fish in.
Ok, onto plunking. Plunking isn't a "dead beat" version of fishing. It can be, but as stated above all fishing can be. I was raised a plunker. First rod I used was a fenwick 89c with an 5000c fishing for steelhead on the Puyallup in the early 70's. It's as much an artform as drifting/flyfishing, etc. Anyone can throw out a piece of lead and sit in a chair. But it won't always get you fish. But, if you know how to read a slot, use the right gear/tackle, and hit the run right and it's extremely productive. Also, as said above, if you're stuck fishing the bank on a big river you can't go wrong. A flyrodder would have a hell of a time casting that much line and controlling it (except maybe spey) and a driftfisherman would be out of their league on an extremely wide slot. Also, plunking is one of the most productive methods when the rivers out of shape. Your bait gets down and stays in place.
Didn't mean to sound snotty, but plunking isn't all brain dead. It is as sophisticated as one makes it. You can't judge it by a few guys you may have seen on a bank. Of course, I also knew alot of guys who would sit and sleep (usely from a drunken stuper) while they plunked. Yet I also knew alot of guys who I learned from who used it as a very successful form of fishing. It produced when other methods failed. So, I will not demean plunking by no means.