It seemed to happen after they posted the SpaceX article(www.theverge.com/2015/6/29/8863121/spacex-falcon-9-rocket-explosioauses) that was poorly thought through. They got some criticism(but not abusive) feedback in the comments.
They started deleting comments in that thread and it all went downhill from there once people realized posts were being removed.
Kinda a shame, I liked Topolsky & Co but I don't visit it nearly as much after that.