Golf's Dirty Secret

Hello. What's the one golf issue no one wants to talk about?
My thought is it's slow play.
Could you go up to someone you don't know and say, "Excuse me sir/madam, but I think you're a slow golfer"? Hardly. The response would be denial or anger. It could become a life-threatening situation.
Even saying that to someone you do know is a scary proposition. That's why, as a marshall, I know someone in the group knows they're slow, yet won't say anything to the culprit. They're not ready for the confrontation. They want me to say it, which I have no problem doing.
Could you do what they do in the show "What Not To Wear"? Go up to a person who's with family and friends and say "You need a wardrobe makeover"? Would "You need a speed makeover" do the trick? I think it could work.
The big issue is most slow players don't know they're slow, just like most alcoholics don't know they have a drinking problem. Once It's brought out into the open, half the battle is over.
Please let me know if "outing" someone would work.

Regards,
Steve