TATE, you have a good way of looking at it when you say that it's a matter of where you draw the line. The Ben Hogan example is a nice story.
That seems to be a good analogy for a situation in pool where you ever-so-slightly touch the cueball with your tip on a practice stroke. When I do that, I always call a foul on myself. Even though it stings to give up ball in hand, it wouldn't sting as bad as knowing I scammed someone out of the ball in hand they are entitled to. The other bright side is that accepting the punishment makes it less likely that I'll repeat that mistake again.
For those who said they don't call the obvious fouls on themselves, would you call non-obvious ones? I'm talking about the ones that your opponent would have no reasonable way to know about, that no one would have called a ref over to watch. For example, the practice stroke that touches the cueball so slightly that the cueball doesn't move.
Regarding someone shooting the wrong ball, just for the record, I wouldn't feel obligated to warn him. IMO, offering information about a foul that
I know I did make is completely different from offering information about a foul that
I believe that they will make. One is being honest, while the other is coaching.
The only thing I don't like about it is having to tell the guy afterwards that he fouled. Unfortunately, when a human makes a stupid mistake, the tendency seems to be to blame anyone else but himself instead of reflecting to find the true cause of the mishap. Immediately, it tends to make the person look at you like you're trying to pull something shady on him, when it's not that at all. Of course, there are ways to tell the person they fouled without making him feel stupid, which is a courtesy I am always happen to extend to him.
This is, of course, JMO, and it could possibly change in the future if I heard a persuasive enough argument.