And if everyone lives by that principle, no one will have a good life.
That is the problem here. Exceptional egocentrism destroys things. If in grandparent's case everyone was sending their children to public school, it wouldn't be anywhere near as dangerous, as there would be a lot of "good" students. These would quickly balance out the bad ones, improving the situation.
Taking out the good students, and leaving the bad ones among themselves is what causes schools to become bad. Many egocentric people use "it's not my responsibility" excuse to wash their conscience clean, and you end up with system that cannot properly function, starts to become massively inefficient and many people who could have had a good life among the "bad" students if they had a decent environment in school lose out because they don't get.
That's the reality of it. You can wash your hands off it, but it certainly doesn't make you a good person. And fact is, when there are too few good people in the world, it goes bad for EVERYONE.