This post is just what the title says: a rant. It was really bound to happen at this point in the semester as everything is coming due at once and students begin to realize how much they have left to accomplish with just 2.5 weeks left. I'm in that position myself, so I feel a little bad about my rant ... but not bad enough to call if off.
Imagine sitting down to grade a paper. In your first sweeping glance from top to bottom of the page, you realize you can trace rivers of white space vertically down the paper because of the excessive punctuation usage. On further inspection, you see these rivers are created almost exclusively by commas. And you further realize that most of them are unnecessary.
Why can't students use commas?
Actually, I don't really blame them for not understanding commas. Commas are confusing. And everyone uses them incorrectly sometimes. My beef is that my students don't think commas can be understood. I give them a cheat sheet for comma use. I provide them with resources to figure out commas. I offer to talk to them individually about papers with comma problems. But they persist in just sprinkling commas about the page wherever they think they'll look pretty. Ugh!
My point is this: Even punctuation has visible consequences. When I look at that first page described above, the message I get from that writer through the visibility of that page is: I don't know how to use a comma and I don't care enough about this paper to get help.
That's why the visibility of even something as trivial as punctuation is important.