When it comes to specific facts and techniques as with multiplication it is very simple though the real teaching involves recognizing where it applies. But when you look at the kinds of truth religions and the humanities are concerned with, indoctrination amounts to a kind of template or filter for understanding interactions, a text or events. It may only be a kind of trainer wheels as for a bike where one is expected to eventually transcend the use of extra support. But the truths of what the world is, who we are and why we are here are not reducible to simple facts.
What the world is is reducible to simple facts. Why we are here is a philosophical question that implies a creator, and so automatically assumes a god already and isn't useful. Who we are is humans.
Philosophy approaches questions like this in a way that's not indoctrination. You can learn how different thinkers have addressed these things. Philosophy classes generally aren't indoctrination because they're not pushing one worldview on you without having you question it.
Indoctrination involves being shown the ropes and critiquing various approaches .. unless one is taught very harshly that there is only one way and the cost of non compliance is catastrophic. So some kinds of indoctrination is harmful but some kind of indoctrination is needed to become fully human.
Indoctrination does not involve being shown the ropes and critiquing various approaches. That's the whole point. That's education, rather than indoctrination.
Indoctrination is the second one, being taught that there is only one way and you need to accept it uncritically. That is harmful. No indoctrination is necessary to become fully human. "To become fully human" isn't even a helpful phrase, as it would need to be established and defined first.
