Surely libertarians do in reality accept that the government has some role to play?

In any case, trying to demonise people because of their views on the role of the government is pointless. I'm sure leftists aren't out to cause a moral breakdown by stealing the fruits of peoples' labour and encouraging poor people to be lazy. Likewise, I'm sure the Christian right aren't all lacking in compassion and wanting to keep the poor down just because they don't agree with the idea of handouts. At the end of the day, this isn't a class war with the poor and the rich vying for power. It's about promoting a system of government that they believe will work effectively for the good of society as a whole.

IMO, the need for various sizes of government various throughout history. It's not a case of big or small government always being good, the effectiveness of either approach is going to depend on a huge variety of factors whether they are social, economic, political, or whatever. For a pretty random example, the more centralised government which emerged in Europe throughout the medieval era and into the early modern period of history was clearly important in creating stable, prosperous states. But as the real wealth moved to the seas with the discovery of the New World and what not, then the protectionist policies of the absolutist monarchs and their support for the old feudal order became a barrier to progress and development.

The ideological associations of the big/small government positions has also changed a lot throughout history. Once upon a time, it was libertarianism that was the radical thing to be. And conservatism was much more associated with protectionism, the nationalisation of industries, the welfare state etc.