I hate it when people say "there was no such thing during the middle ages" about things like this, with such arrogant assurance that they are right. It's making a broad assumption based on popular notions of what the middle ages were like.
And sometimes, it's making a specific statement based upon research.
Now, this isn't something I've done extensive research on, so I'm not going to make any definitive claims, aside from the fact that 'secularism' did not exist as a word until well after the middle ages. However, it is my impression from what little research I have done that:
A. Some of the underlying thoughts and philosophy existed around the time of the middle ages, BUT
Was in each case at least one of the following:
1. Non-European
2. Extremely late period, more getting into the Renaissance, and not accepted until LATE into the Renaissance
3. Pre-medieval and generally either ignored or reinterpreted in the middle ages
4. Universally condemned, and probably all the writings (and possibly the writer) ordered burned (well, I don't know if the writers were actually burned -- but put on trial and their writings burned, in any case)
5. Not at all about freedom of belief