Two points:  1)  It can't hurt to show an example of the plagiarism and might stop people from asking, and 2)  People could at least stop wasting their time looking for examples to show these idiots; they can just refer them back to the ban PM. 

I also don't like the way "spam or plagiarism" is written, as it might come across as ambiguous to a banned member.  I think if it's spam the message should say that.  If it's plagiarism, an example ought to be shown in the PM.  My suggestion would not make anything worse and might help--the question is whether it would be too difficult to implement a change like that and whether anyone with the power to make the change agrees with me.  Probably not, so I'll stop suggesting it.

So OP is a liar with his incoherent denial--what a shocker.  Usually plagiarists tell the truth, and I'm disappointed in you, OP.