Maria - I absolutely agree, well said. I'm also grateful, especially to my dcs primary school. I trust the teachers there, which I can say with relief after my, well, astonishment at the incompetence and alarming, unaccountable behaviour of the last Steiner class teacher we had to deal with.
She was unusually bad, granted and our dc's first class teacher, at another Steiner school, was likable, approachable and competent. There are good teachers in every school who succeed in spite of peculiar 'pedagogy'. Even so, I'm certain that anthroposophy can't but disable rational thought and your point about a possible notice over the door was a brilliant stroke! We play with these things at risk of our dc's futures and there are worse risks, outlined in this thread, which we can't ignore.
Also: in a Steiner school your child is stuck with their class teacher for 7 years! Sounds like an interesting idea unless you feel, as several children I know do, that the teacher dislikes you for some unknown, unfathomable reason and that nothing you do is good enough.
It would be a shame though to inhibit diversity in education. Plenty of people are unhappy with their dcs schools, with reason and not all children suit large community colleges. There's room for improvement! But you're right, we must apply the same care to these alternatives as we would to any regular school. We certainly shouldn't be hood-winked into a failure to do so by trusting in vaguely understood concepts like 'spiritual' or 'natural'.