Being negative and being an asshole is not synonymous!
Believe it or not, it is completely possible to disagree and/or be critical of someones idea without being a jerk or an asshole. As we all know, emotion, intention, and connotation are all hard to convey in a text-only medium. Take a bit of extra time to ensure your comments are polite and respectful, and always keep in mind - PERCEPTION IS REALITY.