You are comparing two different animals. One was, essentially, a family based unit for economic and military purposes, the other is a romanticized social club, for people who love their Scottish ancestry, history, etc.

The modern Clans are more like Rotary or the Elks than they are like their old namesakes. People join to make connection with other like minded/interested people who are their kin (whether they are or not). They can get together, dress up in a kilt, have a meal, talk about history and the like and think they are a clan. But few if anyone that belongs to one today feels any fealty to the Chief. No member of a clan is going to have taxes levied on him, or march off against the Campbells. That was the old Clan.

The Old Clan system you speak of is in the same state as Carthage, and was in the days of your Grandfather. It was done in on Drumossie Moor and buried by sheep. It lives only in books and the imaginations of members of the Modern Clans. So, if you want to, you can take it less serious and join an association.....or not. Membership in a Clan is no barometer of your love of your heritage.