I also agree. You'll be able to discuss what's in this week's preview next week, when the next episode comes out. (A mouthful, I know.)

A lot of people don't watch the previews. Those of us who do can be patient and wait another week to rant. If a person who doesn't watch previews knows that in the current episode discussion people spoil the next episode for them, they may be discouraged to participate in the discussion.