People often say, "while I disagreed with you on this topic or that", as a prelude to explaining why they find themselves in agreement or in support of another's point of view. You'll see plenty of it today as people mark the death of Christopher Hitchens.

In truth, we all do this and it's a rather bizarre thing to do. As though we need to justify our shared belief in the topic at hand. 

I find that I disagree with pretty much everyone at some time or another. I rather suspect this is true of every human being on the planet. The question isn't whether we disagree on this point or that, but in whether we find common ground more often than not. Perhaps more importantly, do we find common ground on the things that are truly important, the things that really matter to all of us?

In the end, maybe what matters most is that we are communicating and engaging in the flow of ideas.