Christians are my brothers and sisters.. so long as they are Christians rather than "christians in name only". If they are not Christians, they are still my 'neighbors' and are due respect. I just don't coddle people by supporting their 'self-esteem' via condoning their false beliefs. It's one thing to be nice. It's another to be truthful. Friends tell you the truth. Shallow pretenders lie to you in order to stroke your ego for their own benefit.
United we stand is scriptural though - Tower of Babel. Didn't work out too well. When you mix clay and mire, they don't stick and rather tend to crumble from the irritation between the two. That is the nature of current circumstance. Unity for the sake of unity is folly. The focus of unity must be on Scripture and Christ's message or there is no real unity. And that does not exist.