DMcG, I'd sack any science teacher who told his children that any theory was true, or that they'd better believe something they were told

How precise are we being? I would, I agree, sack any teacher who insisted a theory was itself an absolute truth rather than the best approximation or description of all we have observed to date. But I don't think I have heard of a science teacher who starts every class with a declaration to that effect. No, throughout all the classes and throughout the year he or she says this "is", or this "isn't", which perhaps the occasional diversion into explaining the best approximation stuff.

Or mine did anyway!