Modern Ethics... Postmodern?

I just finished the session on Modern Ethics, which leads into the water of postmodernism.

I honestly don't know exactly where I stand in regards to the modern vs. postmodern discussion. The main tenet I have at issue with postmodernity are described very well by Gerard Reed, known as epistemological skepticism and ethical relativism:

"We cannot know "truth" regarding objective reality, the Postmodernists say, so we "construct" it in either individual or social ways; we cannot know what's universally right and wrong, so we determine, on a subjective level, how we or one group choose to behave."

I have a really hard time with these concepts, mostly because of the mass amount of relativity that it involves. It really begs the question, if there is no knowledge or morality beyond an individual or groups subjectivity, then what is the point of trying to live a life on arbitrary standards, or laws? What is the point and purpose of believing or following some way of life, when it is all a matter of relativity? What does this relativity say about morality? For me, it basically says I can do whatever I want as long as I don't infringe on the individual subjectivity of another persons life. As Jack Johnson puts it: "It's all relative, even when you don't understand." For an individual's life to be guided by his or her own volition, his or her own subjective reasoning, with nothing else to base it off of seems like a scary proposition to me. I am interested to further my knowledge on these ideas.