Far too often a moderator will delete comments from one side of a conversation while leaving comments from the other side of the conversation in place.
If it were a series of stand alone comments and one particular contributor was off-topic or rude that might be understandable. However, in many cases deletion of one set of point/counterpoint comments leaves an incomplete, out of context, incoherent series of remarks utterly lacking the other side of the story, while still tagging the deleted user by name.
Two options are preferable to this practice; simply push all comments to chat as is often done, or delete the entire conversation. Anything less can only be construed as selective censorship, laziness, or both.
So what, if any, reason is there to delete one half of a conversation in comments and leave the remainder hanging if what's left is incoherent and doesn't serve the purpose of comments?