The reference adds stuff like the author, journal or year, so it can be a showcase for the relevance, importance, how new is it, etc. I still find it useful in cases like the presentation not being followed by a paper, or you add visual aids that are not present in the paper yet are not your own work.
Disagree. They showed their arguments, and those seem pretty valid to me, even though I disagree. IMO being open, transparent and promoting community discussion is a good sign.