I think there are two parts of the debate... One, if it is a good idea to disrupt a playoff run by trading an important piece for future assets, and two, whether or not posters value the closer position.
I think many people that disliked the trade, or felt like it was a bad idea at the time, believe that closers are instrumental to successful teams, and others that believe that closers and saves are similar to RBI, and is really just a matter of circumstance.
I don't think the closer position is that important. I think that the reason that great teams often have really good closers is simply because they have really good bullpens, and often the best guy in the bullpen pitches at the end of games and racks up a lot of saves.
With that said, the trade made me pretty nervous at the time. Precisely because of what rick150 points out above. And not just the affect of irritating the other players, but by irritating the fanbase. What is easy to forget as time moves on, though, is that Hader's bad spell prior to the trade was REALLY bad. I'm sure management was worried about his torpedoing any trade value he had. At the time, I didn't like the trade, but was hopeful that Rodgers would be good enough, and that the prospects ended up working out. In hindsight, I think the trade still hinges on the success of Gasser. The Brewers didn't know they'd be able to turn Ruiz into Contreras+ at the time.