I’d like to try and explain why, if we think all morality is subjective, why we do not just let everyone do what they want.
Let’s take Persons A through D. Let’s say…A and C are theists, and B and D are atheists.
How do these people interract? Well, we don’t want people to come and steal our things…and it’s probably better that we all help each other, trade goods and so forth. So, let’s hire Person E to be our police - E can arrest those that go against our moral code.
Hang on, though - A-D don’t all have the same moral code. A, for example, as a theist, may want people who blaspheme against their deity to be arrested. C agrees. B and D do not - they don’t believe in that deity, so why does it matter if you say bad things about them? On the other hand, B is very much in favour of abortions. C is too - C’s religious, but believes that abortion is still morally correct ( up until a certain point). A and D are very much against abortion - A because of his belief in a deity that says it’s bad, and D because she believes that a fetus is as living, and has the same rights, as we do, logically. Should abortionists be arrested? Argh! They cannot decide! What can they do?!
Well, they can compromise - A and C might agree that the police should not arrest blasphemers, but in return, B and D might agree that police can arrest those who stir up hatred against religious groups. Likewise, A and D might come to a comprimise with B and C as to the time of the pregnancy at which a fetus can still be aborted. Hooray! They’re in (relative) agreement! E can now arrest people, and, in general, people will be happy with this arrangement. They’ll disagree with some things inevitably, but on the whole, more people are happier.
So, along comes Hitler (Boo! Hiss!). His moral positions are not the same as A-D either! They’re just as subjective, though - they are no more wrong or right than the others! So, what can we do to him, if he is not, objectively , wrong?
Well, Hitler’s actions and beliefs are seen to be subjectively wrong by A-D. So, laws against him are passed, and he is arrested! (Hooray!). Four people are happy - A-D are all very pleased, and they feel happiness. One person is sad - Hitler’s not gonna be a happy bunny in prison. Overall, then, what’s been achieved? Well, four people are happy, one person is unhappy. It’s a victory for (subjective) morality! Hoooray!
I realise this is a simplification - Hitler’s arrest is also good for many other people who may be killed in the future because of him, plus it gives the families of those killed, as well as strangers who are morally opposed, happy thoughts. Likewise, there’s going to be more people who are unpleased - Hitler’s supporters aren’t gonna be happy. But I think you’ll understand my general point - morality is subjective, but a group/culture can still act in accordance with a comprimise of all their moral beliefs to counter those who disagree with them on one of those general comprimised beliefs.