What makes a man a knight, is not his tools but his fortitude and understanding. The knowing that he never stands alone even when he has fallen, that his sword shows compassion equally to death, that what must be done is not always right, a man who can show kindness before and after a war to his enemies, but never during, to have honor and pride but never force upon them the job of the crutch, to have respect for all things, and to hold truth, honor, loyalty, reverence, and courtesy above all material things. That is what makes a knight. (to me any way)
As for the armor, it was there for a few reasons.
1) No man does nothing (to defend himself) if he wants to live.
2) Knights under the system of vassalage were worth protecting as they are key to the social ways of the time.
3) It was not really a symbol of the knight, many have worn armor and never had the title.
4) The first reason.
5) Reason 1
6) Reasons 1,4,5
Ultimately, knights did not parade themselves around in full harness (unless at tourney). However, in the today many would not assume you are a knight if you didn’t have armor unless they were familiar with historical textiles and wears.
I know this is an old subject and I am quite late but that is my thoughts.