While it is true that those with O- (i.e., Rh negative O blood type) ideally should receive O-, if there is a shortage of O-, women who can't bear children and men will be given O+. There is a small risk of transfusion reaction with the Rh factor, but even if it occurs it is generally a mild one, unlike the life-threatening reactions one might get with ABO incompatibility (i.e., type O receiving A,B, or AB; type B receiving A or AB; or type A receiving B or AB). The reason Rh negative women of childbearing potential are excluded from receiving Rh positive blood is to prevent Rh immune sensitization and difficulties with future pregnancies. Also, please understand that transfusion reactions can still occur even with "compatible" blood types, due to the wide variety of red blood cell antigens know to exist.
Dr. W.
Thank you for sharing your knowledge.