Scholasticists were careful though not to overstep the dogmata and say heresy. Discussing heresies was very much allowed, as long as they were considered heresies and thus wrong by definition.

Different churches at different times and places were more lenient or more strict, but always kept the One True Faith which could be discussed but not put to doubt. At least, this is how it looks to me after some superficial reading about the topic.