Basically, it isn't. The theory that everyone should do a little bit is based on the idea that if 1000 people each solve 0.1% of the problem then we solve 100% of the problem. Which in general isn't a bad idea.

The problem comes when somebody tries to sell it with bad math. Because then you have a hundred million people each solving one trillionth of the problem, which accomplishes effectively nothing. And worse than nothing, because then you have a hundred million people each thinking they've done their part and no further action is required, even though no one has made the slightest dent in the actual problem.