It doesn't matter that Earthling is a good guy. Like ATPG said, he just confuses everyone and annoys people while he's alive, frequently hurting the innocent team. In every game he's been in in which the innocents suffered defeat, he was at least partially responsible. In LOTR, he was probably mostly responsible, at least ignoring the parts where Camikaze (The GM) screwed up slightly and gave Isengard and Mordor some help he probably shouldn't have given them.
In LOTR, he continously had shouting matches with other innocents, especially Bad Player, and kept repeating his completely-false conspiracy theories. He tried to protect Autolycus (Mafia) at one point. Admittedly, he at least had a decent reason for that, even if it was plainly obvious to everyone that Auto was mafia. Later, the shouting matches started draining energy from people like Winston and Renata who didn't want to deal with it any more, making some of the innocents just start losing interest in the game. Eventually we lynched Bad Player, Earthling, and Takhisis (who was spamming and arguing with Earthling earlier, and ended up being one of the only ones we still thought could be mafia), all innocent, in rapid succession, costing us the game.
In NOTW XXXIII, he was an innocent scanner. He acted like... well... Earthling, and got himself lynched, depriving us of a scanner. Eventually we all died. To be fair, we got a long way even without him, and him not dying might not have made much of a difference, but... still.
In Star Wars, he and Renata were Han and Chewy, two innocents with a decent amount of power (obviously). They actually came up with a decent scheme at the beginning, then Earthling ruined it by telling everyone about the scheme, spending 2 days trying relentlessly to kill Niklas with walls of text, and ended up getting them both killed. Renata even decided to quit because of Earthling's play style, then the mafia killed her anyway. Granted, he did manage to get the innocents all knowing each other, so I don't blame him much for the innocent loss in the end, that was more due to the later mistakes made by the other innocents, mainly Nictel and Bad Player. He did, however, screw up a lot at the beginning.