Here's the map of districts of those Representatives (click to enlarge):
This immediately reminded me of the map I posted regarding attitudes toward pantyhose in this post. Here's the map from that post:
Just to see if the two might be correlated, I physically combined the maps (click to enlarge):
[Edit 10/8/13 -- added this map, below]
Here's the same data, but this map only shows the relative prevalence of people who believe it is "acceptable". Red indicates very high prevalence, yellow indicates medium prevalence, and blue, low prevalence. (Click on map to enlarge.)
I think the correlation is striking, though certainly not perfect especially in certain regions. For example, the region of East Texas and West Louisiana is a stronghold of the Suicide Caucus but is very pro-pantyhose. Likewise, we'd expect Suicide Caucus members in Nebraska, Oklahoma, South Dakota, and West Virginia, but there are none (at least indicated by signatures on the letter). Also, the most pro-pantyhose region of Colorado is in the Caucus, and likewise with Idaho.
Food for thought and grounds for further examination.