Tone of voice and body/facial language have a lot to do with how these things are taken, too. Not that your words aren't important, just that they aren't the entire thing. Many times the perception of being negative or mean or conceited, etc... is just from the way something is communicated, not the communication itself.
How many times have you been told something you already knew? Was it easier to hear when you were told with a snobby attitude or a cooperative one?
You can stick up for yourself and what you believe without seeming negative towards other people. It just takes some of us a little more effort than others. I've definitely had to "practice" that one myself.
