It would create some level of accountability, similarly if they're going to keep downvotes - showing who did it could add value; if retaliation is a worry by people downvoting, then perhaps they should reconsider not adding a downvote - and simply letting a comment fall away, or consider putting effort into writing a comment, using critical thinking to explain the dislike, as opposed to satisfying and processing their urge via a quick click of a downvote - which benefits no one.