Gadolhadorah,
“If the average frum yid is accepting a certain hashgacha, someone who wants to step above the “average” can only be machmir by relying on a non-mainstream, ultra-conservative hashgacha”
Let’s not be so cynical. It’s been my experience that those who are “machmir” have reasons for doing so, such as not relying on a specific kula that an agency allows. Many therefore do rely on “mainstream” hashgachos for many items (same as other agencies!), but not for foods where the problematic kula is applied.
None of this has anything to do with derech eretz, mitzvos bein adam l’chaveiro, or spousal obligations. In fact, letting one’s own insecurities generate resentment towards other Jews who may be more stringent with specific halachos is in itself a violation of a mitzva bein adam l’chaveiro. Seriously, just get the chalav Yisroel, pas Yisroel, yoshon, heimishe hechsher, or whatever for your friend, use disposable/sealed packaging as needed, and show some love and respect, and you’ll find that you get it right back.