Is it Okay To Ask Thanksgiving Guests to Bring Food?

This year, we're going to have around 15 people over for Thanksgiving.  I was talking to a friend of mine who gave me the brilliant idea to have guests contribute to the meal.  Not so much the turkey but things like salads, bread or pie and such.

Then I was talking to someone else and they said that it's bad manners to ask guests to bring food.

Really?  I don't think I would be offended if someone asked me to bring something if they were hosting.  What do you think?  Leave a comment and let me know.