Let me get this out of the way first: Robert Griffin III is one hell of a quarterback.
It doesn't matter. It's a bad deal for the Redskins. There are times you go all in. This is not one of those times. It strikes a desparate chord on the part of Mike Shanahan.
NFL draft picks are not created equal, but all have a significant chance of going bad: they are more like bets on a roulette wheel than they are sure-fire franchise players (or starters, for that matter). The fewer bets you have--or in Shanny's case, the more you take from yourself--the less likely you are to get lucky and hit on something.
The laws of probability dictate as much, no matter how much cognitive bias (hyperbolic discounting) you apply to the draft. You simply can't get around the fact that four chances give you a better chance than one. In short, if you give up three first-round draft picks and a second-rounder for the value of one pick, you had better be completely sure your single pick will yield more fruit.
Yet, as we have seen so often (anecdotally and statistically), the draft never allows for this kind of assurance. It's not possible. There are simply too many variables (players, schemes, coaches, teammates, injuries, etc.) in play to accurately predict the future of these draft picks--no matter how much hindsight you apply.
Just how sure does Shanny have to be about RG3 to have justified this trade? A simple (and rather crude) thought experiment will suffice.
Let's say Shanny is even 90% sure that RG3 is a franchise guy. Okay, great. Mark it, Dude. The Rams would only need a 22.5% chance of any one of its four draft picks going beast mode for the trade to be worth it (each pick is mutually exclusive of the other).
I'm sure given Shanny's massive ego, he probably puts the percentage at 100%. Even so, the percentage goes up to 25% for the Rams' picks. I like the Rams' chances here.
Certainly the argument is more complex than this. Quarterbacks are worth more to their teams. In addition, the Rams aren't going to draft a quarterback with any of their four picks, so it's hard to compare apples to oranges. Lastly, a second-round pick has less pure value; picks in future years have reduced present value. This is all true. However, it hardly removes the larger points from the discussion: the Rams now have more lottery tickets; none of us truly know what RG3 will become.