Alignment as many issues to deal with, but there is one that I am not sure has been commonly raised. Would a PC or NPC actually identify itself as evil? From an objective moral standpoint, we could say that an action is evil. We could evil call certain people evil. But, would these “evil people” actually call themselves evil? Yes, there are occasional individuals who do use those labels, but it is extremely rare. Even if a person is committing human sacrifice, they are not doing it with the thought that it is morally wrong. They are doing it because they think it is morally right. Professional assassins do not identify as evil either. They are simply making money performing a service. If someone hires them to kill someone else, that person probably deserved to die.
In the PHB, Gygax argues that assassins must be evil because being paid money for killing sentient beings is evil. As an objective moral truth, he may be correct. However, it makes little sense to think that PCs would identify as evil even if the player selects an evil alignment. Monsters would be even less likely to identify themselves as evil.
The AD&D rules treat alignment as objective moral truth as well as self-identification. Yet, it is virtually nonsensical to claim that a sentient creature would identify as itself as evil. Right actions are the ones to be done and wrong actions are the ones not to be done. When orcs raid human villages, they do not think they are committing a wrong. They think they are doing something that is right. In other words, orcs or any other “evil” aligned entity is likely to call itself and its actions as good.
I would suggest that an altruistic and egoistic axis to replace the good/evil one. Then you could have an order-freedom axis to replace lawful/chaotic. An orc or assassin would be viewed as extremely selfish thinking its needs outweigh the needs and rights of humans. This would resolve many, but not all of the issues. At least in terms of what most PCs will encounter in typical D&D games, this would make more sense.