The problem isn't so much tightening it as releasing it. Many, if not most, accidents occur because of some sudden, completely unforseen event, to which you must react instantaneously if you are to avoid disaster. Somehow, the idea of something mechanically holding my throttle open while I try to take emergency action just doesn't sit well with me.
An auto-throttle that releases when you touch the brakes is better, but that's expensive and complex.
I've added a "throttle boss" to my Kuryakyn grip. That's just a protruding bit on which I can rest my palm as I motor along, eliminating the need to hold the throttle open. But when I let go of the throttle it snaps closed, as G-d intended it to.
