@Reconstructo,
Just thinkin' out loud here:
What are some positive traits of an argument?
1) It establishes its conclusion as true
2) It persuades or convinces the reader.
3) It's clear, coherent, short, and stylish.
There's more, I'm sure.
What are some necessary traits of an argument?
Only the first one above. A secondary purpose of making an argument may be to persuade, but if it fails to do so, the argument is still a good argument if it establishes its conclusion as true. It's nice to have a clear argument, but it's not necessary. It's nice to have an argument that persuades, but it's not necessary.
I think it's a bad idea to call a fallacious argument a good argument just because it manages to persuade someone that the conclusion is true.