If all you did was an entry level "bar exam, it'd be pretty much useless. A newly graduated CompSci student, is really just an apprentice, who may then (if they continue to work hard, and are given challenging work) go on to become a master craftsman/journeyman over the next 5/10/20 years.

The same is true of those other fields too really - I certainly wouldn't want a newly qualified doctor operating on me, or lawyer defending me, or civil engineer designing a bridge I'm driving over. It's nice to know that someone has been professionally educated and passed some entry level exam, but to be useful in a field it's experience that counts.