Being a teacher requires making decisions. Teaching worldviews, as they relate to human history, requires very difficult decisions about the level at which to have the discussion. This is because people, even entire nations and cultures, are never self-contained and self-consistent with their own basic worldviews and outlooks on life. So we can either focus on the actual practices of a given culture, which will often be messy and chaotic, or we can focus on the ideologies or larger worldview, which is in theory self-consistent.
So when I teach about the "Judeo-Christian" tradition as the foundation of Western culture, and contrast it with, say, the kind of modern progressivism of the late 19th and early 20th centuries, it looks like a simple contrast. I am painting with a broad brush, and I'm doing it purposely. I am contrasting the ideals of Christianity with the ideals of progressivism. How those ideals are actually implemented may be a messy affair.
In my Sunday School class yesterday I made a sustained argument that the progressive worldview, for all its emphasis on hope and a coming future utopia of peace and prosperity, actually involves tyranny, bloodshed, and death. On the other hand, a Christian worldview rooted in the intrinsic dignity of each and every individual human life leads to human flourishing.
Broad brush? Yes, of course. And at least one member of my class interjected a perfectly fair point: the "Christian" West has plenty of sins of its own. The brutal subjugation of native peoples was one particular example, as well as the African slave trade. This is partly why having a discussion at the level of worldview is more helpful. And I'll put it here as succinctly as I can:
When, for example, Marxism/communism leads to the death of millions of people, it is being consistent with its worldview.
When more or less Christian nations abuse, subjugate, and enslave people, they are being inconsistent with their worldview.
Put another way: What Christianity calls sins, progressivism calls virtues.
This is why reform movements have been successful in the West. When William Wilberforce or the northern abolitionist movement railed against the sins of the West, they did not call upon people to reject its Christian worldview; they called upon people to greater conformity with the gospel. The "sins" of the West is not an argument against the worldview of Christianity; it is an argument that the West needs more, not less, conformity to its worldview.
So the broad brush argument, at the level of worldview, is not hindered in the least by the fact that Christians have often failed to live up to their ideals. It is an argument that we need to stress and proclaim the ideals even more persuasively and forcefully.