*Or, rather, why this is a really stupid (and unlikely) idea.
Since all the Phillies' hitters have simultaneously contracted bubonic plague and are unlikely to survive April, much less an entire season, the theory of the day is that the team should explore the possibility of trying to trade one of the team's pitching assets (or Domonic Brown) to shore up its perceived weak hitting. Besides, the People Who Demand That Something Must Be Done are demanding that Something Must Be Done.
These hyperventilating fans (straw man alert!) are suggesting that the Phillies need to git them some bats! And yesterday! Hamels, Brown, Blanton, and Lee have all been suggested as bat bait, but let's just duck Brown now, since that raises all sorts of other problems, like, you know, the future and stuff.
I wrote about 2,000 words about this in two stabs at this theme, but it really boils down to this: Scoring runs alone doesn't matter. Preventing runs alone doesn't matter. Run differential matters. The larger the run differential, the better it is for your team. No, really. It's that simple. Hang around here for a while -- this is a topic we all circle back to repeatedly. It needs to be revisited from time to time, even though I would rather be writing "Phillies All-Time Playoffs Heroes #5: George Brett's Hemorrhoids."
A poorly-conceived trade doesn't help increase run differential. It is hard to imagine a set of circumstances where a trade, right now, could be arranged that would not be a bad one for the Phillies. I'll work out the specifics below. I note that Petzrawr did the Lord's Work on this recently, shooting fish in a barrel, but there's a lot of stupid out there to fight, so I'm all for piling on here.
Before we get to possible trade targets, let's look at where the Phillies are now. They gave up 529 runs in 2011, which was the lowest number of runs allowed by any team in MLB since 1969. That was a staggering accomplishment. They did not need to pound teams into submission, a la 2008. Suffocating them quietly was just as effective (actually, it was more effective because they were better at suffocating teams in 2011 than they were at beating them to death in 2008). It seems more humane, too, somehow. I think of Cliff Lee smiling kindly as he holds a big pillow over Chipper's face, sending his soul to Cthutley to devour. It just seems like an appropriate and welcome ending to a spent, weary spirit. Besides, it would probably be comforting since Chipper and the Braves are already used to choking. 
Any attempt to help the Phillies win more by trading pitching to get a bat must result in a larger run differential to accomplish the stated goal of helping the Phillies win more games. Any hitter(s) obtained for Cole Hamels, for instance, will cause the Phillies to lose Hamels' rWAR of 5.4. Maybe the Phillies get an internal replacement pitching performance from the next body in line for the Starting Pitcher 3 slot on the depth chart that results in 2 WAR if they are lucky (Kendrick? Blanton?). But the obtained hitter has to hit (and field) for the team to make out on the deal.
To net a gain out of a Hamels trade, the Phillies need to get back a player that would generate more than the remaining 3.4 WAR to break even. It would take more WAR coming back to make the trade result in a net gain, without even getting into contract/salary cap considerations. Maybe 4.0 WAR? Any less and it's pretty much just noise. Really complicated, right? The new player has to be better than what you give up. See, this is really hard, isn't it?
The 4.0+ WAR would also have to play a non-blocked position, so not center, right, shortstop, catcher, first, second, third, or...I guess it has to be a left fielder, huh? Here's your list -- pick the guy you want over 4.0 WAR who the Phillies could pry loose. Ok, maybe nobody is really available. Let's get creative. How about a third baseman, and then the Phillies could move Polanco to second till Utley is resurrected, okay? Here's the list. Ok...maybe a RF could be converted for use in LF. Here's your list. Which of any of these players do you think is able to be had for Blanton? For a rental of Hamels? Jose Bautista, right? Justin Upton? Evan Longoria? Are you high?
Then knock it off with the trade talk. Besides, Hamels is going nowhere.
 You young 'uns missed some great times.
 That's just your pride, Braves fans.
 I'm obviously using WAR as a proxy for runs added/prevented. I think that's a fair approach.