"...in coming freshmen, who literally do not know how to hold a baseball to throw it."
I wondered if anyone else has had this experience! I am constantly amazed by this.
When I used to coach Little League, my first year I was several games in to the season before I realized what the kids were doing. From then on, it became point # 1 at practice # 1 to teach the 4-seam, 2-finger grip.
There are two things at the root of this. First, many youth leagues actually teach a 3-finger grip or a whole-hand grab to very young players on the reasoning that "their hands are just smaller." I can only imagine that someone who never played thought that up. Because with two fingers and a thumb on the ball, you can control it no matter what your hand size. It's the same principle as a 3-legged stool.
The other root of the problem is that kids are constantly told "there is no one right way," or indulged in doing what they find most comfortable. When it comes to grip, there is indeed only one right way (unless you're pitching). If you tell a kid to go with what's comfortable, he'll do what he's always done, because anything new feels uncomfortable at first. (Some kids will even mess up their throws intentionally to try to get the coach to let them go back to the way they have always done it.) The cure is to force the kids to throw correctly so that it becomes what is comfortable and automatic. The younger the better; it's easier to start off right than to go years building bad habits and then try to change them.
Note that a key part of that second thing is that the kid is being encouraged to disregard and disrespect the coach and his instruction. Now, if we could solve THAT problem, the world would be a better place. But instead, as you note, we have parents setting the example of disrespecting the coach.
The one advantage to high school ball is, you can cut those kids. I say, let's do that --and let them and their problem parents do their grousing from their sofas at home!