Unity comes from understanding. But agreement is not a requirement of understanding or unity. Many of the issues tackled here are serious and envoke passion in people. And these are not weak willed people on this forum, so when the sparks fly they tend to fly high.
But again, I don't think that shows a lack unity. Just the fact that we come here to learn, teach, discuss, debate, (and occasionally sling shit at each other ) I believe shows a profound sense of unity. We argue about these issues because these issues matter to us. That's what unites us.