Guess its up to the person shooting the gun. Will a .243 kill a deer? Yes, is it the best choice? In my opinion No!
Anything that will kill a deer will kill foxes, yotes and groundhogs...with that said, I'd prefer to use something a little larger for deer. To me, a .25 cal. (.25 WSSM, .25-06, .250 sav. to name a few) should be the min. when hunting deer. Just my opinion!