These ngrams chart the positive and negative uses of terms associated with political rule, suggesting the extent to which, in Britain, France and Italy, monarchy increasingly confronts discussions of despotism and tyranny.  The exceptional case is Spain.  For the most part the negative terms are well established 18th century terminology, often hailing back to the classical world (in the case of tyranny) or to discussions of forms of rule in the early to mid 18th century (as with Montesquieu and the discussion of despotism).  Terms such as autocrat are much more modern. 

What we find, in many cases, is that monarchy continues to have positive associations - after all, it remains the standard model.  But criticisms of political rule can draw on the languge of despotism and tyranny to characterize the threat they pose to citizen's liberty, without necessarily being anti-monarchical.