You'd sack any teacher for saying that a theory was true, Steve. But you cite Galileo's house arrest, which actually happened more or less for that reason. There was no problem with his proposing a theory about planetary motion, but he insisted on saying it was true, rather than provisional, which at the time it actually was. (And I'm not defending his house arrest, even if he was being a wee bit unscientific. The Church had no business getting involved in controversies about science.)