You weren't right - because they STILL are idiots. All the more so because they do not think there is anything wrong with the downright abusive chanting in the first place i.e. that it's all part of the banter - when in reality, it can be hurtful and offensive to anyone, not just the player to whom it's aimed.
But there's nothing wrong in my view with booing the ex-player or ex-rival player and no need to eat humble pie when they end up playing for you. Banter in sport is part and parcel, quite entertaining and adds to the spirit of rivalry and competition. In football some players get a thrill out of it and it actually encourages them to play better - kind of like assuming the pantomine villain role. It's almost flattering to that player i.e. when Adebayor was getting booed by Spurs fans while at City, shows how much he affected us by causing so much damage during games and would only encourage him to want to score against us. If Chamakh (for example) were to leave for another club, the next time we play against him I doubt he'd get the same level of boos.
On another note I'll admit that I never liked Adebayor before he came to us, but the only problem I thought there might be (and still do) is to do with his commitment rather than him being ex-Arsenal. I didn't like him for the attitude that he seemed to have, but mainly because he wouldn't stop bloody scoring against us!! :)