maybe you should read what a clan is:
http://en.wikipedia.org/wiki/Clani know that a clan in terms of online gaming is not the same, but it basically derives exactly from that.
also you should read up on banners.
in short it is about representation, not socializing. therefor banner- or clanhopping is not about representing but just leeching. some people allow it, others dont.
by representing a clan you advertise whatever that clan stands for/achieved and earn further prestige according to the clans general agenda. in most games this is a two sided thing where you are basically just accepted for one side because they see each other as mutually exclusive. in crpg/warband you dont have just 2 sides, but still some factions that exclude each other.
considering that this game is about teamplay, it is not important which clan/banner/faction you are in. reminds me of that merc who tried to command the public mob on eu_1 years ago, sometimes successfully. and there are others nowadays who can rely on people following them just because they are recognized in battle. (representation!)
For me, it's interesting to discuss about this in a scientific way
a forum full of trolls is the worst place to go for that. talk to social workers or something similar.