This issue has plagued my own WordPress sites for years. I finally had enough of it and took the time to fix it. I was surprised at how simple and easy it was to fix. That means this is going to be a quick and easy tutorial! All you have to do if find your theme's functions.php file and append the following code to the end of it:
//remove smart quotes from posts:
//remove smart quotes from comments:
...and that will stop quotes from being converted in both posts and comments on any WordPress website! Have fun posting code that your readers can easily copy and paste now! What is really cool is I went back and checked some of my former posts that I made before I implemented the above code and it changed all those quotes back to plain simple quotes too, so it is backwards compatible!