It wouldn't be such a bad idea if there weren't IDEs that would help you review your code more easily.

Think of a text document you would scan for typos. Sure it would help you to print it out and read it on paper. But finding them with words auto correction is much faster.

This kind of auto correction is also present in IDEs (integrated development environment / the program you use to do the actually coding). You can also jump from one part of your code to another part for a quick lookup or analyze it with its help.

So printing it out not only doesn't let you editing it it also slows down reviewing / debugging / refactoring it.