The argument has much to do with the modern development of technology, which enables governments to be more distructive and intrusive. It also has much to do with the "decadent" characteristics of monarchy after the Wars of Religion: Monarchs no longer sought to compel their subjects to think or believe in a certain way, and they were increasingly uncertain about the security of their thrones and, hence, more inclined to compromise.
When a form of government is not too sure of its authority, it's also not inclined to do much damage, but it shouldn't be assumed that that form of government is inherently and essentially less dangerous.