Make the assumption that there is no purpose in life. A chemical reaction happened to make something that lasted. Some more chemical reactions caused that to morph into something else which was able to self-propagate, and so on, until after a billion years of snowballing, you’ve got life. There is no greater meaning.
Regardless of whether there’s a meaning or not, I’m still stuck here living my life. If I’m enjoying myself, then I have no particular impetus to change the status quo. So long as I am living, in fact, I may as well do my best to enjoy the experience.
But, this is just as true of everyone else. We all want to enjoy ourselves, and that’s one of those things where more is always better. But say that for each of us, our idea of enjoyment is growing up to become an astronaut. Well, at the moment, it’s infeasible for all 6 billion people on the planet to become astronauts. Due to scarcity, for every pile of happiness some percentage of everyone has to get the shaft.
Now yeah, we could just duke it out until the population of the planet was low enough that everyone who remained could get everything they ever wanted and a pony besides, but fortunately we’re smarter than that. We can’t all have everything we want, but we can get enough so long as we figure out rule systems for fair competition. None of us has any apparent right to say that they’ve got more right to anything than any one else. If we both want the last iPod on the planet, killing each other over it is stupid. We pick a method of competition – e.g. financial – and the loser just has to accept taking a behind-the-times CD player instead.
The big rule, though, is that I have zero power versus any other individual. I can’t force you to do anything. I’m not greater than you or more important than you. If you piss me off and ruin my happy, that doesn’t give me the right to kill you. The rules of the game are decided by all of us via some means that we agree upon as being fair (i.e. representative democracy) and policed by people who we agree upon as arbitrators (i.e. police and courts). Just because you’re pissing me off doesn’t mean that you’re doing something wrong according to any reasonable rule of the world. If everyone had the unilateral ability to decide the rules – “Talk too much and I’ll kill you” – we’d have chaos and no one would be happy. I wouldn’t be safe myself in such a world. In order to be happy most of the time, some of the time I’m going to have to suck it up and co-exist with people who piss me off. To some percentage of them, after all, I piss them off and I’m fairly sure that I don’t consider myself as worthy of death or any other punishment.
On the other hand, we are all individuals. Some of us care more about being an astronaut whereas others couldn’t care less. We could simply dole out everything equally, but that wouldn’t really work very effectively. If you give me a Barbie Doll and a video of porn, then I’m going to trade the Barbie Doll away to a little girl in exchange for video of porn that was alloted to her. Now she has two Barbie Dolls and I have two vids of pornography – we’re both happier than we would have been if we’d simply split everything evenly. So when we do split up all of the joys of the world, we want something like a bidding system.
How much does each person have to bid with? In our modern world, that’s determined by how much they’ve done to make others happy. If you were willing and capable of busting your ass and becoming a doctor, society will give you a bunch of chips to bid with. If you figure that you’d be miserable if you had to work hard and are happier as a lazy bastard, so you become a cashier at a porn shop, then you get less chips, but hey you’ve presumably made the choice that maximizes your happiness. Getting the extra cred with the rest of the world wasn’t worth it to you.
Now if there was an actual all-knowing, all-powerful God, then he’d be able to come in and truly maximize everything. He could make us all astronauts who wanted to be, if he was willing to be a giving soul. Or, he could at least divy up all of the world’s joys at the true perfect ratios instead of the closest approximation that a global market and modern system of representative governance allows. Unfortunately, if he does exist, he didn’t even bother to suggest either of those systems when he wrote his big book, so there’s not a ton of evidence that he’s a giving soul, let alone a very thoughtful one.