Hell doesn't factor in. It's not about punishment. It's about what we measure our acts against.
The reason we use tools as symbols is because we believe goodness can be measured through our acts. But for a tool to be effective it needs to be two things: universally adopted, and based on a mathematical constant.
The measure of a cubit, for instance, is the definition of relativism. It's divergent for everyone. If everyone agrees to use the Royal Cubit, however, it can become a useful tool, and if people agree about what's right or wrong, the social contract, that too can become a useful tool.
If a bunch of builders are building a temple using the Royal cubit, they'll all be working together, but if one says "screw it, I'm using my own arm length!" then his blocks won't fit. But why is he wrong? Because the greater good isn't served? Because it didn't accomplish everyone's goal? These are all contingent on the universal acceptance of that this building was supposed to look like, which is entirely opinion. He says one thing, they say the other. Who's to say which one is right?
What about pharaoh? Maybe it's wrong because pharaoh says so. After all, he's the one who ordered the temple, and will execute the builder. So pharaoh examines the block and decides he likes the different one better. So now the rebel was right and everyone else was wrong, because the pharaoh changed his mind.
See, right and wrong are entirely dependent on what goals we agree to. And we can adopt universal measure, if we can work toward the same goal, but who sets that goal? Society changes its mind all the time. Pharaoh changes his mind all the time. And we change our minds all the time. Right and wrong, without God, is merely convenient preference.
That's why we use mathematical constants in Masonic philosophy. The length of a 24 in gague may be subjective and defined by humans, but a right angle is not. Degrees may be just a number we pulled out of our collective asses--90° is totally subjective--but a right angle isn't. It's the Pythagorean theorem. It's unchanging. It is what it is anywhere in the universe, and neither our rebel builder or pharaoh can change it. So if the builder tries building a temple using his own personalized notion of a right angle, it will collapse.
That's geometry. And that's God. God is our moral constant. Why is murder wrong? It is wrong because God says it is wrong, and no one is changing God's mind. God had a purpose for the universe and for us. This purpose is universal and constant, and because of those two things, measurable concepts like right and wrong can exist.
If there's no God, then it isn't wrong, it's just your opinion.