The biggest reason i'm fine with trading Hallahan is that i think it's extremely unlikely his situation will change at the end of 2015. The only reason he got games this year is because we had a massive amount of injuries. Even if that somehow happens again in 2015, Anderson, Whitey and JOR will be added in 2015, meaning Hallahan will have less opportunity. Even at best case for him, he plays half a dozen games, which i don't think is enough for him to not ask for a trade.
Add that to the fact that we need to free up a couple of spots on our list, and i don't see how trading a depth bloke for something of value is not the right decision. My other thought is, how many players who can't force their way into a team after four years (despite being healthy for the last two, albeit in a top team), then go on to be the kind of superstar who can lead a midfield? I'm sure there are examples, but if we foresee him being just a solid, bottom 6 of the best 22 type player at best, then we should see what we can get for him.