I have been in clans since the Kali Doom days. 15 in all. But I dont see what your seeing. You say you see clans as condesending and arrogant to newbie players? A large majority of clanner and non clanner alike are condesending and arrogant to newbie players. So you shouldnt say its just clans. Even the Solo players are just as arrogant. If you want proof then check back in the history of some of these forums and look for the "Stupid newbie question" then read how many flamed the newbie. I am willing to bet an equal majority are non-clanners.
As for the best part of clanning. That is teamplay plain and simple. In team based matches you need clans. Now I am not talking FFA. I mean CTF or fortress style games. Ever tried to find a good team match on a pub server? Its a rare occurance. You only get real teamplay when you play with a clan. On a pub server you always get two or three morons that think they and they by themsleves will win the match and all others need to stay back and watch. Those are the ones I see die in horrible ways about 30 seconds after they made that decision.
But clans are better in FFA or DM type games too. If they know what they are doing that is. Go set up a four player room, find two clanners from the same clan that has played the game since it first came out, find two non clanners that has never played together or barely played together but played the game since it came out also and stick them in that server then see what happens. The two with the TAG will almost always come out with the most kills. I am sorry but its true. I would always put my money on the guys with the TAG.