A) The thread got a lot better quickly; the last post I saw when I opened it was the "All Sanders supporters are dumb" post before I posted (well, I saw that post, then had to go off and do a few things, and then posted in PoliGAF without checking back on the thread). Hence my frustration at the thread - it felt more like a "bash Sanders and his supporters" thread rather than any kind of actual discussion. The military part comes in because it's a very obvious counter-argument to the "BernieOrBust people all have more privilege" than me. Just like Sanders' policy weaknesses would disproportionately hurt minorities over whites, Clinton's policy weaknesses disproportionately hurt enlisted folks (who are predominantly poor and minority). The fact that folks were arguing with a straight face that the first was unacceptable but ignoring / unwaware of the second...is like a blind spot some Sanders supporters have of racial minority issues. The hypocrisy of the argument at the time bugged me.
B) Overall I pretty much agree with you (in my case, hispanic culture / experience is the one I'm really lacking, since I've had very little experience on that front). In that thread at the time, and as often in identity threads on Main OT GAF (and other places), I think it turns not into discussions about gaining perspective and sharing experiences but using their identity as a club to beat people over the head with and try to show how virtuous they are. I enjoy actual discussions, but in the OT threads that I see that are tied to identity politics, in my experience, tend to have a lot of folks using social justice as a cudgel for being an asshole and it being "OK". (The Trump thread where folks were justifying actual fucking terrorism because they were minorities might have done it for me).
"Identity politics", like "SJW", are terms that are like tools. How they are used and what they stand for is very much based on the wielder and the observer. (I say this as what might be called a SJW myself, but more of a SJ Cleric, because NO ONE EVER WANTS TO BE THE FUCKING HEALER). Do people use SJW as a pejorative to be an asshole to someone? Absolutely. Are there fanatics (especially online) who go way too fucking far and deserve the pejorative usage of that term? Absolutely.
Or, in longer, better terms, what I try to work on myself (the ending is what makes it all spot-on)
http://slatestarcodex.com/2014/09/30/i-can-tolerate-anything-except-the-outgroup/
Anyway, sent you a PM if you wanted to keep discussing and not derail the thread further.