Thank you Mr. Durden for raising this in meta. I haven't been entirely comfortable with the conflict in the comment stream, but I haven't been sure how to address the underlying issues. Your question in meta helped me to clarify those issues and my vision for what I want SE to be.
Are sources required?
I think your summary is absolutely spot on:
It is about the philosophy of the site, whether we are going to make it clear that sources are not required. . .
You assert, ". . . information page for this Stack Exchange site says that sources are not required . . ". I'm not sure which information page you are looking at; with my tongue in my cheek, I'll point out that it would have been easier to respond to that if you had provided a source. My best guess is that you're referencing "Links to external resources are encouraged. . . ". That is somewhat less conclusive than the way you phrase the admonition, and it appears to be a stock/default phrase on the corresponding page of many help centers.
I don't think sources are required; I'd be a hypocrite if I believed that, since several of my answers are unsourced. I think sources improve almost any answer. I think sources are vital, possibly even critical when addressing contentious topics. Sources and methods are and essential distinction between history.stackexchange.com and politics.stackexchange.com, or discussion.stackexchange.com.
One of the things that makes history history - is that when we hit a disagreement, we analyze sources to see how strongly they support our arguments. If we don't reference sources, then my opinion is just as good as yours, and we're merely discussing things. I'm not interested in trading opinions. I think there is ample evidence in the help center that H:SE is intended to be a Q&A site, not a discussion site. There is no way to assess the quality of an opinion. There are common methods to assess the quality of research and analysis.
At the core, I think this disagreement originates in the first comment that I saw from you - you said something along the lines that one must deploy logic first, and then seek out evidence; I replied that I thought the obligation was to employ research first, and then test the research against logic. That fundamental disagreement is echoed in your comment to
@litlnemo above "What people need to do is THINK..." I think there are contexts in which your approach is appropriate. I am afraid that I don't think that it is appropriate for H:SE.
You cite Soviet history books as an example of invalid answers - I completely agree with you. That is precisely why I want to know the sources that inform your answers; I need to be able to critically examine them. @Anixx has cited Soviet documents to support his answers. I believe @Anixx has a first rate mind and is a better researcher than I am, but when he cites Soviet sources he applies a different critical frame than I do. I apply a different standard of scrutiny to answers that cite Soviet sources than I do when he cites other sources. The fact that he cites his sources enables me to evaluate the answer. You don't give me that opportunity - because you don't cite any sources and are hostile to the notion, I have to evaluate all of your answers against a very skeptical standard.
I've read enough of your answers to know that they are thorough. The problem is that without sources, I can't tell whether they are trustworthy, accurate or reliable.
Self appointed police
Guilty as charged. As the SE about page states, "It's built and run by you . . ." We collectively curate this site. We vote up and down, we comment, we review. We discuss our shared vision of what the site should be. I believe that answers with sources are better. I believe that when an answer touches on contentious topics, sources are essential. When claims are astonishing, sources are essential. If we collectively decide that sources are not required, then I'll back off. (I think the current guidance is probably good, although if someone were to suggest some language that we could insert specifically on the H:SE page, that encouraged sources, I'd support that)
Here is the crucial point - if the community tells me to shut up and stop demanding sources, I will. The community has taken me to task in the past, and I have changed my behavior.