Ok, allow me to straighten a few things out. I am playing the C-G ranger in question. Please allow me to enlighten you on the situation as it really happened....
Firstly, no one in the party actually said that the Rogue should keep the contract as his own...it's just that no one else wanted it.
Next, the rogue is the character that didn't word the direction to the Glabrezu correctly that got the villagers killed. My character only noticed a hand sticking out of a sack that the Glabrezu was carrying. Also, let me point out that this was the 4th session in said dungeon, and my character was not in the original group that entered the dungeon. Not to mention that the DM doesn't re-cap all that much. So, once he informed us that all the villagers were dead, i remembered that they were the reason that were in said dungeon.
Next, The party was getting owned, and after the rogue got dominated we were in big trouble. Once the monster that dominated the Rogue was killed, my character grabbed the contract because no other character was able to do so at the time (and no one else wanted it once again). After the fight was over, my character asked the Glabrezu to help us out of the dungeon that we were in. At which time the Glabrezu tried to kill us all by taking a Month to get out of the dungeon (not uncommon for a Glabrezu).
Next, The DM asked what my character was going to do with the contract, and i replied i'm going to study what the monster is and then probably release it back to it's home plane.
Lastly, the DM then decided that the session was over and began handing out EXP and that is the point in which he informed me that my character was changing alignment.
My only problem was that i didn't understand what my character had done to have to change alignments. I will say that YES there were clues, but only very subtle clues that made sense in hindsight. If I am completely out-of-line than I am sorry. Maybe i need a better understanding of how alignment works.
So, i guess my question is...What did my character do to deserve an alignment change?