One advantage is herd protection. Kind of like like herd immunity from vaccines. But less accurate.
Let's take that arbitrary 1 million number. It's as useful or useless as any number, but it gives us something to work with. If any percentage of that number takes the recreational course and test, then that percentage will have learned something. For what percentage of the "1 million" will actually get it, who knows? But since we started with an arbitrary number, I'm going to say 10% of the people who buy a junk affordable drone from the Sharper Image catalog will actually go the motions of taking the recreational exam. So, of the 10% who go through the course and exam, 10% get it.
At the end of the day, you have 10,000 people who know it's wrong to fly over people at a low light and you shouldn't dive bomb seagulls (some idiot on a sister forum). And that's 10,000 people who have a decent understanding of where and when it's legal to fly a drone.
So when you are flying somewhere, doing the right thing, and someone starts to complain; there may be one of the 10,000 there who will have your back. At least in the US.
If anyone from the FAA is reading this: If you want increase the number of people taking the example, give them something for passing. People love stickers and they are cheap. Give them option of a shirt or mug that says they passed the recreational exam. Just a suggestion...