Frank, the use of the semicolon is never (as far as I can see) required for joining two clauses. It's a matter of the writer's style.

Now, suppose I left out the parenthetical and said, "The use of the semicolon is never required for joining two clauses. It's a matter of the writer's style." Okay, you'd buy that, and it's perfectly grammatical.

But suppose I as the writer feel that those two clauses really amount to one grand thought, more closely related than merely two different statements of principle. I might want to indicate that closeness by using the semicolon. If I were speaking that larger thought, my speech cadence would indicate that closeness, and I'd want the written form to show that.

I know you don't like it, but it's not wrong either way.

In a way, I see the semicolon in that sentence as the equivalent of inserting ", but instead", joining the two parts of the combined thought.

The only sin would be to do a comma run-on to accomplish the same end.

I assume you are not criticizing the use of semicolon(s) for a complex series. If you are, then we've got a serious disagreement.

Dave Oesterreich