In the case of Pharoah's birthday, it was to show that a good thing happened to the cupbearer and a bad thing happened to the chief of the bakers. It was this spared cupbearer, who told Pharoah about Joseph the interpreter of dreams. Because Joseph interpreted Pharoah's dream he was made a ruler in Egypt, second to the Pharoah. And because of this, Joseph's family, during the time of famine, were given land in Goshen by Pharoah. This same Pharoah and the Egyptians held both Joseph and his father, Jacob in esteem. See Gen. chapter 50. So, how sinister was this Pharoah's birthday celebration? In the case of Herod, that a bad thing happened to John the Baptist on Herod's birthday--all done at Herodias' instigation. Do you think it wouldn't have happened other than at a birthday celebration?
Now, how would you view it if nothing bad happened on those birthdays? Would you be at liberty to celebrate them then? Is the birthday celebration evil or what happened at the celebration? And what if I give a birthday party and unlike Pharoah and Herod order no one to be executed? How have I done something unscriptural?