I would argue that they were far worse for two reasons: dissension from orthodoxy in Inqusition Spain was not illegal - dissension was accompanied by unconscionable disabilities (being forbidden to own real property except in certain restricted areas, ineligibility for various offices and honors, disqualification from numerous professions, exile, etc.) but torture and death were circumscribed to dissenters who concealed their dissent.
And of those accused, more than 75% were acquitted by Inquisition courts and freed by their own recognizance.
A disgustingly brutal and immoral system - but enlightened compared to Stalinist Russia, where the very fact of dissent was fatal and every trial ended in an execution.
Their religion just didn't have a theology.
At this point we're begging the question - since professing, as Element187 does, a "belief in science" is a religious profession as well by the vaguest definition.
But your larger point is well taken.