Using 'They' As A Singular Pronoun

Some criticize those of us who use 'they' as a singular pronoun because it is allegedly grammatically incorrect. I have to admit not really minding if it is grammatically incorrect because it is for a far greater cause (rather than using 'he' all the time when reading the Bible for example). It seems, however, that using 'they' as a singular pronoun isn't without its precedents.