The rules and values are arbitrary, yes. Maybe they are conditioned, or socially imposed, or even just an illusion. How we got them does not matter. It only matters that we do, in fact, have them. And that “fact” need not even be true in the material sense. So long as it is true phenomenologically. For our philosophies need only be humanist. Because when we say “our” we are referring, of course to ourselves. Here is where I make my first assumption, and it is a metaphysical one: assuming that “we” are what we experience, or at least this is what we our concerned with during our lifetimes.
Now, why it matters that we do, in fact, have rules and values, even if they are arbitrary. Like the rules of any game are arbitrary, but there is still a way to win and lose. Chess, for example, has rules. The knight moves in an L-shape, the game is over when the king is “checkmated,” and so on. Now, arguments about why the rules of chess are as they are would be fruitless. In practice, it would be ridiculous for a player to spend mental energy thinking of “why” the rules are as they are. Instead, he must devote all his psychic powers to his next moves and defenses, if he hopes to defeat a formidable opponent.
Samely, there are rules to life generally. You must drink water to survive, sex creates new life, and so on. This may seem obvious, but consider that it just as easily could be otherwise. Our material (or what appears to be material) universe is mostly predictable and only slowly dynamic. This is what Hume discusses about being thankful for the order of the universe. So my philosophy is this: remain thankful for the order and the phenomenological nature of the universe, and play by the rules to win the game.