I thought this was interesting read. Slightly long, though. http://www.sbnation.com/longform/2012/12/13/3758698/rick-barry-underhand-free-throw-nba
Why should "under-handed" be considered more embarrassing than "ham-handed?" Then you gotta check the scoreboard, too.
I'm still confused as to why no one uses the backboard on free throws. Using the backboard, you can literally make every shot as long as you aim for the square...it's that simple.
Under-handed is not embarrassing if you make 90%. Any form is embarrassing if you can't make at least 60%. Any reasonably athletic person should be able to make 60% given enough practice.
Science agrees. Using the backboard at a 52 degree angle provides the optimum chance of a make. The limitations come from how free throw shooting is historically taught and learned, not from any sort of perceived human limit on accuracy.