The thing that worries me with him being drunk, is I could see him being destructive. He was destructive when he was drinking. Personally, Me, my fiance, the guests, nor the staff need this problem. My mother wants me to trust that she'll take care of it, but she's willing to wait until he starts drinking. I don't want one single drop in him.
I'm sure he'd be complaining about it during, and after the wedding, but that won't last forever. He should be lucky he was invited.
What really blew my mind was when my mother told me she was worried about one of my friends drinking. He's not an issue, since he's an incredibly happy drunk.