The GP does have a good point though. A D, even if it's a failing grade, means "you didn't pass, but you came close. Just try a little harder and you can pass next time," whereas an F says "You weren't even close to passing. You really need to radically rethink your study strategy and/or go into a different field."
I don't recall ever taking too many classes where I didn't know roughly how well I was doing long before the end of the class. Doesn't a student typically already know if they were close or not to passing? The test you got back with a 54 or the homework you handed in for a 62 or the quiz you got an 83 on all gave pretty exacting performance metrics. Most classes I took in middle school and higher even had introductory handouts on the weighting of the different types of assignments/tests so that I could calculate my final grade in advance.
If a student were operating in a bubble without any indication of how good or bad they were performing, then you and the GP would have a point.