I feel like showing the number of votes a comment has gotten will lead to people voting something simply because it's gotten many votes and that must mean it's right. You see it happen all the time on Reddit. Someone will say something that sounds correct, and before someone else can come correct them they'll get a bunch of upvotes. Partly because they sounded correct, and partly because "all these upvotes must mean this is true".
I don't really see any benefit to showing votes on comments.