You know, THIS is the problem (and I'm sorry you had to be the one I quoted, 6iron. You're not the only one guilty of this.)
It's about time some of you guys grew some balls. That's what this campaign is about. It's not just about getting slow players to play faster, it's about getting YOU, the avid golfer who both plays AND watches golf (and subsequently will see the commercials) to step up and add some peer pressure (and education) for the less experienced golfers, many of whom don't know any better.
The reality of the situation is that probably no less than 25% of the time, the people would be offended that you confronted them about it and may get confrontational. And I think 25% of the time is a conservative guess. People don't like being called out by their peers. If somebody official-looking does it, they might grumble under their breath about it or wait til they leave to complain. If I do it, there's just as much chance he tells me to mind my own business, chill out, he paid good money, etc., as there is he says "okay thanks, we'll do our best."
And it won't matter how nice or calmly you approach them. Either way, at some point you have to ask them to play faster. You're assessing blame, and putting it squarely on their shoulders, in front of a group of people, some of whom could be family members. Why do family members matter? Because sometimes a father feels the need to display his manhood around his sons, etc. And there's also some cultural barriers to this. I've come across a group of golfers of a different nationality that became very offended when I asked to play through once. Some consider it an effrontery to be approached that way. In American culture, it's more about emasculation than effrontery, but it results in the same type of confrontation, more or less.
It's analogous to law enforcement. Sure, any and all of us can tell that crazy guy to stop loitering or vandalizing where he shouldn't be. In all practicality, he'll tell us to f**k off because we have no authority and he knows we can't do anything about it.