Different people prefer different calibers. A 243 is capable of taking deer cleanly, but the margin for error is greatly reduced. Some have even used it effectively for black bear or other game (be sure to check you local caliber requirements). However, we can't control all the factors like wind gusts, deflection, animal movement and bullet performance. IMO, there are other calibers with low to moderate recoil that offer better to much better performance on deer sized game. Hypotheically speaking, if a person were to shoot 100 deer with a 243 and would then shoot the same 100 deer with the exact same types of shots and weather conditions and shot placement using a 30-30, 308, 7mm-08, 280, 270, 257 Roberts, 257 Ackley Improved or similar cartridge the second 100 deer would provide cleaner/quicker kills. Unless things have changed recently, some states and ranges do not allow the 243 for deer hunting.
Personally, I consider a 243 to be a varmint round that is capable of taking deer sized game. Because of this, it is a round that I personally don't like for deer. Our family has shot many 2 to 3 year old beef steers using a 22LR for a head shot. However, there is again a very small margin for error. Some years back we moved to a pistol caliber carbine, which works much better.