The problem specifically is that they are not the ASCII quote character. There is only one ASCII quote character, and that's the one used by programming languages. Any other quote or quote-like character is outside the ASCII range, and must therefore be Unicode (or another non-ASCII code page).
I know they're not compatible with programming languages that you may want to use. But that's the languages' problem. They're perfectly valid, standardised, characters.
Not exactly the same. Since anything inside ASCII quotes is typically considered a valid string in most programming languages, if you delete everything after the final quotation mark you have a syntactically valid program. It won't do what you want, but it's not a syntax error.
So unicode quotes and ASCII quotes are not exactly the same in this scenario.
They both break what you were trying to do, and the fact that they do it in slightly different ways really isn't worth making a long pedantic argument about.