If morality is invented, can we complain about moral wrongs?

I'm reading Plato's Republic (the Bloom translation which is a rich and beautiful literal translation - Bloom's opinion is not thrown onto the original language) and just finished the discussion on justice between Socrates and Thrasymachus and oh, what a discussion it was. Thrasymachus believed justice was the means used to establish law for a city. He didn't hold that justice is actually a virtue, instead he held that man creates justice or invents justice to satisfy his own arbitrary law which then makes justice the "advantage of the stronger" or what makes something "advantageous to the stronger." Socrates, of course, disagrees with Thrasymachus and embarrasses the rhetorician in their conversation that lasts for quite a few pages. In my understanding, Thrasymachus held that man creates values, instead of discovering values which is colossal to our understanding of justice or morality. What's interesting is that Thrasymachus begins his conversation with Socrates on moral grounds. He claims that Socrates is immoral for using conversations with people to Socrates's advantage, i.e., Socrates asks his conversation partner questions and leads the other person to affirm his own position; Thrasymachus finds this immoral and "wrong." He then argues that justice and the like are man-made and are tools for the stronger. If that is the case, then he cannot accuse Socrates of doing wrong to him or to the city because there is clearly nothing inherently "wrong" about it. Using Thrasymachus's view, Socrates is only doing something that isn't preferable to Thrasymachus; why should he care? If you think about it, Socartes is only doing what is "just" to people, i.e., he is doing what is to his own advantage, which would be "just" on Thrasymachus's view. After Socrates points this out, Thrasymachus rolls his eyes, says something sarcastic, picks up his dolly and goes home. What a child. 

Nietzsche philosophized on going "beyond good and evil" and on morality. He wrote the following in Anti-Christ:

"A virtue must be our invention; it must spring out of our personal need and defense. In every other case it is a source of danger. That which does not belong to our life menaces it; a virtue which has its roots in mere respect for the concept of “virtue,” as Kant would have it, is pernicious. “Virtue,” “duty,” “good for its own sake,” goodness grounded upon impersonality or a notion of universal validity — these are all chimeras, and in them one finds only an expression of the decay, the last collapse of life, the Chinese spirit of Konigsberg. Quite the contrary is demanded by the most profound laws of self-preservation and of growth: to wit, that every man find his own virtue, his own categorical imperative. A nation goes to pieces when it confounds its duty with the general concept of duty. Nothing works a more complete and penetrating disaster than every “impersonal” duty, every sacrifice before the Moloch of abstraction. — To think that no one has thought of Kant’s categorical imperative as dangerous to life! …" 1 

Nietzsche was an existentialist. A lot of U.S. lingo arguably came from the man like "personality," "lifestyle," and "charisma," and it's no wonder since Nietzsche wrote on the human experience. When someone says I need to find "myself" you can think of it as an Americanized Nietzschian phrase. Is it butchered Nietzsche philosophy? Perhaps, but it's very easy to see its roots in his philosophy. I mentioned that because, especially if you live in the U.S., you can think of conversations you've had with others that sound like this: "I need to do what's right for me," "I need to find myself" or "This is how I express myself and it's good for me," and there are others you're probably thinking of that touch on personality, lifestyle, etc. that I can't think of at the moment. Keep those conversations in mind and then re-read my excerpt from Nietzsche above. Do you see it? How Nietzsche wrote that man's being is the ground for his own virtue or morality. "Virtue must be our invention..." If virtue is invented then it's not binding on every individual and it has no weight. What does that mean? Well, taken to its logical conclusion it means that nothing and I do mean "no thing" is actually wrong. It's totally preference based, like your taste in skateboards or clothes. If morality is invented then murder, rape, slander, and the like are totally preferences and not binding on all mankind whether we acknowledge it or not.

it must spring out of our personal need and defense I wonder if this is the chaos of Nietzschean philosophy? When Nietzsche declared the death of God he was arguing that man had, to use a phrase of my generation, gotten over God and moved onto something new. Man didn't need God anymore. However, man still wanted to use God's morality or Christian morality, which left Nietzsche in wonderment. He called them "pinheads" and argued that you cannot kill of God and still use his moral standard because you killed the standard. You took out of the foundation of the building and expect the building to not crumble? What a pinhead. So there's this chaos after the realization that morality no longer grounded. What does man do in the chaos? Well, Nietzsche taught that during chaos some of the brightest, most influential, and creative ideas emerge from the creative men. So we must create a new world basically. To use exaggerated language. So we need chaos to create a new world; to create a new morality. One that is man based. This is the heart of existentialism: man before essence. “Virtue,” “duty,” “good for its own sake,” goodness grounded upon impersonality or a notion of universal validity — these are all chimeras, and in them one finds only an expression of the decay, the last collapse of life, You cane hear the heart of the existentialist in this sentence. A morality grounded in universal validity or in an impersonality wreck the human condition and the longing of man. Such a grounding takes away from man's existence. In the next thought Nietzsche clearly expresses his moral relativism: Quite the contrary is demanded by the most profound laws of self-preservation and of growth: to wit, that every man find his own virtue, his own categorical imperative. Nietzsche argues, seemingly, that you cannot find objective morality in natural selection, instead you find quite the contrary; you find selfishness which is totally opposite of what our moral faculties discover in nature. He then goes on to declare his moral relativism which necessarily flows from a morality built upon naturalism evolution that "...every man find his own virtue, his own categorical imperative" (a jab at Kant). If you have a naturalistic moral foundation then the logical conclusion is moral relativism. You cannot escape it. You can try, but it fails every time.

If morality is created by man, then we cannot complain about immoral things because moral things would not be facts about life. When you argue that morals are relative then tell someone he is morally wrong you are putting objective morality in the closet when it suits you then grabbing it out of the closet when it suits you, which is completely dishonest; you are being a Thrasymachus, which isn't cool my friends. If you are in the moral relativism camp then stay there. You cannot have it both ways. Nietzsche, Sartre, and others knew this and had the courage to stay in their camp. Do I agree with them? No I don't, but I at least respect them for being honest (I guess on their view honesty is preference based and not a universal good - interesting).

Source

1. Nietzsche, The Anti-Christ § 11