I'm going to have to disagree (not only with this post but also others). Yes, I agree that raising undead skeletons is an Evil act in the DnD universe. However, this does not mean that Players should not have access to it. Sure, Good players should have to change their alignment to either Neutral/Unaligned or Evil if they do such things (too often).
However, PC's CAN and often ARE either Neutral or Evil. And they should be allowed the opportunity to raise undead things. However, one of the most important reasons why the ritual is not in the PHB is not the above. If it was they would have put it together in the Monster Manual (like the ritual to make a Vampire Lord) or in the Dungeon Masters Guide together with the Evil gods.