Leiter on Smith: Isn't it Ironic, don't you think?

In critiquing Steve Smith, Brian Leiter wrote:  "Of course, we know what intellectual discourse looked like when dogmatic invocations of the deity were thought to constitute an argument.  And there is a reason those cultures and eras were not ones notable for their great number of intellectual insights and advances."  (emphasis added). 

I have a question for Brian Leiter.  Are we are just supposed to accept your version of history on the grounds of your dogmatic invocation of "of course, we know..." or must you support with reasons your argument that the middle ages, for example, was not a time of great intellectual insights or advances?