....you lack. Lacking is the true opposite of having, but today we seem to have been brainwashed by the consumption gods into thinking that if you don't have something, you need it. Need and possession are both related, but are not at all the same.
Once again, I'm being like Indexed and making a graph of things. Now, to really be right about things, this graph would need a third dimension: want. Want is the seed of consumerism. It's getting late, and I don't really feel like going into a great big rant about why consuming is bad, but you can check out the Story of Stuff.
All I really wanted to say is that while we often tend to think that need and have are opposites, this is not the case. I also want to say that "or lack thereof" is one of my favorite phrases. Unfortunately, its formality (or, lack thereof) does not render it very useful when I'm writing essays and decide to throw it in there in parentheses.