It's called lack of (1) writing abilities (2) reading comprehension (3) clingy belief syndrome and the (4) agenda flu. Seriously.
1) Writing abilities
I've debated people on these forums hundreds of times and they've gotten all pissed at me becuase I replied specifically to what they WROTE. On many occasions, it comes out that this is not what they MEANT but they still WROTE it.
2) Reading comprehension abilities
People don't take the time to really READ and UNDERSTAND what you did, in fact, WRITE. They see one or two words in your post and they automatically make a connection to some belief of theirs without really READING your post. I would say the lack of reading comprehension outweighs the lack of writing ability here; but not by much.
3) Clingy belief syndrome
I think everyone is guilty of this. When your beliefs are challenged, most people resist what's being written even more. Unfortunately this usually follows the lack of reading comprehension of understanding what you actually WROTE.
4) Agenda flu
A subject is written about. All the person needs to see is the subject or a word and they have not only a belief system around the aforementioned subject but they have an agenda and want to share it with anyone and everyone. Most recent example is the Kobe training thread. The thread is all about how Kobe trains. Not too many posts in and then you get a number of people denouncing Kobe and the ground he walks on. Just start a new thread on how much you hate him and don't pollute the original thread's subject matter. But I digress...
And these are a few of the reasons why people are stupid and I hate most of them