@Cyracuz,
I would say that the better you know and accept yourself, the less need there is to engage in 'attacking' conflict, and the more interested in you are in other peoples opinions.
Attack born from criticism is done out of fear. A completely self-assured person knows whether or the criticism is valid - and acknowledges valid criticism ...
...and if the criticism is not valid, the self-assured person (knowing that it is not valid, and comfortable with who he/she is) can respectfully and with caring, respond, perhaps with something like 'well, I at the moment I a different view of that, but just so I can understand, why do you say.... ' (that of course, is a very summarised version)
To me, the same goes for differences of opinion or knowledge, though I think in these forums, it becomes a bit of an intellectual game.
The other thing that is removed is tone of voice. You can say things that would otherwise be taken as an attack, in a warm voice, and people hearing you will understand the nature in which it is meant...but the lack of 'voice tone' in written word removes understanding of the nature in which written word is meant, and we therefore have to add words in that suggest tone - which can be difficult to do accurately.
Personally, I have a difference of opinion with JL's signature line. I would have gone 'The spirit of civil conversation consists of exploring the validities of anothers observations, rather than in automatically tearing it down." (or something similar - that's off the top of my head)