Certainly there are many reasons for quitting. Bad round, WGT error, something comes up at home/work, whatever. Regardless, how would making every ranked round, single or multiplayer, have to be completed have any bearing on "the reason"?
I'd venture to say the number of "WGT errors" would drop substantially if this was implemented. If people couldn't just quit and have a "do over", unless it was a computer or personal issue, why would they quit? Further, if they do quit a game, regardless of reason, they would have to finish the round upon their return before being able to play another game. Isn't that the whole point of a handicap system anyway?
I can answer my own questions, because there really is only one answer. That is the only way to effectively remove quitting, and it would be nothing to implement. Quitting would be a non-issue from day one of implementation. It seems to me the simplest and really only answer to the "quitter" debate.
Like I said prior, quitting doesn't really matter to me unless it freezes myself and others out of a round. Generally, I just finish the round on my own, but I prefer to play this game with others. I further, generally play with friends, and I think my friends are like minded and play to the end regardless as I do.
I know I'll never be a really awesome player like Boll, Lee, and a number of others, and I'm good with that. Playing a game with great players in their category is fantastic. Making this change would not have any effect on the truly elite in this game. I suppose a system like I have proposed will hurt people who artificially deflate their average by quitting, and really, who cares. That is actually helping them in the long run, by forcing them to improve. I look at my ranking number as a way to judge my play against what my average would dictate I should be shooting. After all, that i the whole point of a rolling average.