As long as everyone fails, there's no disadvantage to failing because everyone will be a failure. A student once thanked me for failing him because he discovered he'd rather be a pilot and study at a flight school that doesn't require English. You'll thank me too. If I let people pass before their writing is perfect, no one will ever take responsibility for improving after they leave the course. If no one takes responsibility, civilization as we know it will collapse into ruin.
Writing is either good or bad.
If you have any errors, your writing must be bad. If you disagree, I'll change my mind only if you bring me results of an extensive scientific study disproving my argument. Only slackers and whiners would resist doing their fair share of the work, and a fair share is gaining a full understanding of the term's work. I've persuaded three people already, so obviously we're on the right track with this idea. I thought you'd disagree, so I've discussed marking standards with a few of your other instructors.