To what extent is the best purpose of education to indoctrinate?

I wouldn't necessarily call it "the best purpose."

But especially in the early grades--kindergarten through second or third grade--"education is more about indoctrination than education. As you progress through the educational system, presumably you've been indoctrinated--learned a lot of social norms, learned how to work with others, etc.--and more time is devoted to actual content learning.

Many educators would argue that the early indoctrination is necessary for the education to follow, and that's partly true. But much of the indoctrination has to do with societal norms, things that really have little to do with the process of content learning.

I'm not saying that's bad. It is necessary for any society to make sure that its newest citizens understand what's expected of them and how to behave. (You can disagree with what's taught, of course.) But for any society to function, there has to be a common understanding of societal norms. And with the changes in society over the last few hundred years, less of that seems to be happening in the home and more is happening in schools.

Hope that helps.