I have been doing the online thing for a long time. BBSes back in the 80s. Usenet. Chat rooms, tons of chat rooms. Forums. You name it. For years and years.
Sometimes the only contact I have with people is online. Yes, it's pathetic I know, but it happens.
Now to the point:
It is impossible to "read" people online. You may think you can, but trust me, you can't. Most of the time all the little things that help us tell peoples' tone and intent are totally missing in this form of communication. It is a grave mistake to assume that it's the same as real life. Most of the disagreements that happen online are due to one simple problem:
This form will always be incomplete. We must remember this when things go sideways and fights break out. The vast majority of the time we are wrong when we assume the intentions behind what someone says (unless they specifically tell us in no uncertain terms). Most of the time people really do want to get along, but, when missing all of the additional information available in complete communication, breakdowns result.
Let us not fall victim to this. Take a deep breath. The person on the other side of the argument may feel just as confused and may really want to just let it all go too.