@nnoble: If it was my child I'd be pissed off, as I would be for any kind of educational warp applied to him/her.
All indoctrination in schools is a REAL problem.
The oversight person in the school works for the state, but you're right, he should be able to do something about this. About other REAL problems, he can't, because he has to support them.
Best of luck with your one or two rogue preachers, who should be able to do their thing openly and not by corralling kids, as in your example (where did this happen, by the way? Did anybody do anything about it? What did they do?)
About ruling the world: a lot of problems arise because few people have serious input into doing it. I think this is a pretty serious situation.
OK, I hope I've been clear.
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@nnoble: Your example is hypothetical, right? Though I'm not saying that something similar may not occasionally happen.

My perspective is that it shouldn't happen.

I'm somewhat dismissive because there are much greater threats that should be of concern. The rigorous oversight, which comes into play when the state takes it seriously (the state is not asleep), is the source of many of these threats, in many countries. The activity that you focus on is carried out, when it is carried out, by much weaker forces.
As someone wrote, "The state never stops talking." Nor do the major economic institutions (e.g., try to do anything and not get advertised at). The message is always 'consume and obey', and the news is always warped by these interests. In education...do I really have to present examples?

1. It's not ALLOWED to be on the curriculum (I'm not suggesting it should be put there), and is systematically suppressed outside the curriculum.
2. If you want to find indoctrination threats they are all around you. Ever watch TV, anywhere? Let's put things in perspective.
3. Students from 10 onwards are legally forced to attend school in most countries, where they are under much more widespread and well-organized indoctrination than that of the sneaky missionaries that you are worried about.
4. I agree that nobody should HAVE TO listen to this stuff - or to anything else - unless, PERHAPS, in a situation in which it is suppressed.

You can probably get acting or modelling jobs here but it would be difficult - I don't say impossible - to get enough income out of them to live on, unless you are a professional. I've played a couple of small movie roles and you should be able to dig up something similar, but it's unlikely to be solid.

In China this is all mountains out of molehills, whatever it might or might not mean in other cultures. If you disagree with Christians, then argue with them, and allow Chinese university students to do the same, and stop denigrating them as innocent victims. Or do you imagine these relatively few guys are somehow supermen who can seduce huge populations? Europe became Christian for historical reasons that go way beyond the efforts of effective or ineffective zealots. Some of this discussion reminds me of the way in which paranoid Americans, severely indoctrinated by the huge power of media and educational indoctrination, in the early 50s (McCarthy years) unwittingly paid compliments to the few Communists who were about by imagining they possessed superhuman abilities capable of seducing the entire nation. One might as well fear the Devil. Just because the State makes use of censorship doesn't mean that you have to.