'Rules' are simply what observers have noted to be what generally happens.
The 'rule' about commas with defining and non-defining clauses is generally followed because it has proved to be useful.
If I (,) or anybody else (,) chooses to disagree with Pat O'Connor (,) about/on/over the sentence we have been discussing, I do not feel any concern about 'lowering my standards' What standards? Whose standards?
"The party opposed taxes(,) which would be a burden to working Canadians."
Surely, you would agree that placing a comma after "taxes" would change the meaning of the sentence. With the comma, the party would be opposing taxes of any kind, all of which would be a burden to working Canadians. Without the comma, the party would be opposing only those taxes that would be a burden to working Canadians. Well, the same principle applies to the sentence "Vince Carter drives past his cousin(,) Tracy McGrady(,) on Friday night as the Magic topped the Pistons." By setting off "Tracy McGrady" with commas, I am telling the reader that "Tracy McGrady" is a nonrestrictive appositive and Vince Carter's only cousin.
The use or omission of commas allows us to express ourselves in fewer words, which, to me, seems quite useful. To say that I am ascribing too much meaning to commas is to argue against this utility.
Here's another link that seems to back me up.
"John-Boy's sister
Mary Ellen became a nurse after their brother
Ben took a job at a lumber mill.
Because John-Boy has multiple sisters and brothers, the two restrictive appositives make clear
which sister and
which brother the writer is talking about. In other words, the two appositives are restrictive, and so they are not set off by commas." (Source:
How to Build Sentences with Appositives - Appositive Phrases and Sentence Constructions - Building and Combining Sentences.)