There's a big social difference that you might be forgetting about. It's easy to sound like an expert on anything when you have all the time in the world to type a response. All you need is a grasp of proper English and Wikipedia.
On the phone, a response is expected immediately. In person? Whole different ball park. For one, there's body language. There are all sorts of subconscious visual cues to tell how confident one is in what they are saying. Shifty eyes, the way a person leans, and what one is doing with their hands just to name a few of so, so many.
In an argument, one can raise their voice. One can use aggressive body language and express frustration with such.
Arguing on the internet leaves all that out. With enough effort from both parties it can literally go on seemingly forever.
See the below link:
http://www.cracked.com/funny-3809-in...nt-techniques/
Now, I'm not saying anyone here is like that now, but after reading that, you tell me arguments on the internet carry as much eight as arguments in person or on the phone.