Maybe split?

@@ -17,0 +18,6 @@
+</sense>
+<sense>
+<pos>&n;</pos>
+<misc>&derog;</misc>
+<gloss>underclass</gloss>
+<gloss>riffraff</gloss>

Not a conversation I heard personally but was retold. The conversation 
was about nishinari-ku and the election (they elected sb from Soka 
Gakkai). it was something like this:
"下民(げみん)やからな。貧乏な人は宗教に行っちゃう"
I don't think "masses" "common people" work in this sentence. a 
derogatory "underclass" does. "riffraff" might be a little off, I don't 
know, but it seems to be in the right general area.

saito: The lower classes; the masses; the populace; the rabbleしもじも

I'm not sure げみん is the more common reading. Saito only has かみん. There are only 11 examples with furigana in Aozora so we can't read too much into those percentages. Not a common word nowadays anyway. 
I think "riffraff" is the wrong register.
I think the nuance of "underclass" might be too negative, even for げみん. The kokugos define げみん as "しもじもの者", which GG5 glosses as "the lower classes; ordinary [the common] people; the masses."
As long as we lead with "lower classes", I think these glosses are fine.

@@ -16,2 +16,2 @@
-<gloss>underclass (of society)</gloss>
-<gloss>riffraff</gloss>
+<gloss>the masses</gloss>
+<gloss>the common people</gloss>

https://furigana.info/w/下民
https://www.vocabulary.com/dictionary/common%2
0people

I think "the masses" is too ambiguous. Same 
for "common people". I thibk this is more 
obviously negative in nuance (at least げみん)
I thkink げみん is more common

@@ -8 +8 @@
-<reb>かみん</reb>
+<reb>げみん</reb>
@@ -11 +11 @@
-<reb>げみん</reb>
+<reb>かみん</reb>
@@ -15 +14,0 @@
-<gloss>the masses</gloss>
@@ -17 +16,2 @@
-<gloss>the common people</gloss>
+<gloss>underclass (of society)</gloss>
+<gloss>riffraff</gloss>