As I have written a bit earlier, one of the ironies of Schlatter's observation that our own share in evil is not removed by our condemnation of evil in others is that Schlatter laid a foundation for views about Judaism that, at best, were profoundly problematic.
As useful as Schlatter's commentary on Romans can be his views on Judaism (like that of a variety of pre-Holocaust Christians across time and place) are not without some troubles. While a significant advantage in reading commentaries and study of biblical texts across eras and regions has the advantage of widening our understanding of texts it brings with it a risk that we will bring with those the insularity or problematic limitations of each time and place. To put it in broadly evangelical terms, all interpreters will be fallible regarding biblical texts so that there will be some problem in each generation no matter what good may come of an overall understanding of Christian teaching.
In Reformed blogging there's debate between advocates of two kingdom this and unified that but both approaches could be very easily appropriated in a direction that could justify tyranny. We cannot imagine that, as Carl Trueman recently expressed this sentiment, that if we get all the doctrinal ducks in a row that the culture we have isn't capable of cultishness or tyranny.
A rather too swift summary of the above article is that Schlatter's distaste for a variety of things in National Socialism did not preclude an anti-Judaic theology that was able to contribute to anti-Semitic views and actions.
My own convictions have been to take a skeptical view of any nationalist loyalty or ethnic loyalty as such. Boasting in one's race or heritage should not be the basis of an actually Christian practice. The reformation or rejuvenation of a national or ethnic or social legacy should not necessarily be a goal of Christian study, piety, or practice. After decades of observing how people in the United States have been interested in "revival" the aims of "revival" are often, at the end, too bluntly nationalistic or economic to find much confidence in even wanting "revival".
When you spend a good chunk of your life ignoring American Christians who attempt to revive this or that social or political agenda in the process of seeking to understand biblical texts then it's not a huge step to, say, read some of Schlatter's commentary on biblical texts and to also set off to the side a few things that were of his time. Our own era must have its own appropriations and assimilations that a century from now may be seen as rabid and rampant advocacy disguised as dispassionate scholarship. The more we learn about the way the human brain works and how we argue with each other the more it seems to be that much of what passes for "reason" can be a faulty intuition that retroactively seeks a rationale.
In terms of a New Perspective on Paul one of the biggest implications of saying that late medieval scholastics misconstrued and misrepresented Judaism is not hard to grasp in a post-Holocaust world, it's impossible to soft-pedal the harm of a "works righteousness" theology in how that theology became an ideology with social, racial and political implications. This is not necessarilly to say (as I suppose some have already) that a traditional Reformation era understanding of the Law and Gospel must necessarily be anti-Semitic but at another level the question (raised by Jewish thinkers and Christians alike) about how far the diatribe against Judaism really goes in early Christian writings won't go away, not least because even if we can establish that the earliest Christians were not anti-Semitic in the fashion in which National Socialists became notorious the seeds did all seem to be there.
Some scholars might go so far as to say the entire realm of justification theory itself becomes the problem, a bad theology which has been imposed upon the entirety of the Pauline corpus but we're not here to attempt to get into that whole field of dicussion just yet.