I agree completely with this argument. I did a ton of research as to the best temperature to incubate at. About 86F is the natural incubation temperature. I would much rather wait longer and have healthier babies, than get it too hot and risk problems. That said, I don't think 89F is a bad temperature, and it has been proven to produce perfectly healthy babies in a shorter time. I just prefer to err on the side of caution.