This is an odd matter. Nobody discusses the sanctity of John Chrysostom despite his horrible words against the Jews, but we're all ready to condemn Thomas Aquinas. He lived in a time and context of state religion: crime against the Church meant crime against the Empire, so it was ordinary that heretics had to be considered as rebels and enemies of the State. The same vehemence was shared even by other saints worthy of veneration such as Cyril of Alexandria who used hard words against heretics. Don't look at the Church Fathers in the same eyes as we do in our days - first millennium Christians were even favourable to slavery, would you restore it in the name of the Church Fathers? Of course, not! Were they heretics or evil? NO! That was the condition the Church was living in those times, and it was valid in those days to have slavery, as well as putting heretics at the stake. The Church, while founded once and for all by God, is a work in progress as for what regards her power to transform the world - the secular world, I mean - according to the Gospel. And sometimes even the saints, being children of their times, thought according to the culture of their days. I don't see any reason to diminish the value of a saint for those reasons.
In Christ, Alex