This question already has an answer here:
Comments by other users cannot be deleted or downvoted by users such as me. Why don't we enable the feature of downvoting comments and many downvotes causing deletion? Please don't get me wrong. But I feel that too many useless comments can distract the readers from getting to the actual meat. I know there are good comments but there are also many a times useless comments. I understand that which comment is useful and which one is useless can be subjective but I think there are enough experts in this site. Thanks!