I think it’s fine if you’re not sharing, also fine if you flip the item you are dipping on the other side. The issue is when someone double dips the part that was just in their mouth
Is there sauce scarcity where u are?(in my country I don't notice if ppl double dip but mostly families/friends eat out anyway. See next point)
Most places provide enuf sauce tat u can double dip if u want, or others can get own sauce if they don't want ur germs. There used to be sauce dispensers at Macs here, but for whatever reason they removed sauce dispensers there. But Texas chicken has a few branches here n they do hv sauce dispensers(mostly chili sauce tho they used to hv tomato ketchup as well) other places give u packets of sauce, so it's hard to share. Then there's sauce/condiment bowls:
These r mostly everywhere except where the hard plastic/ceramic ones are. No sharing in chinese/Asian culture necessary(unless where these aren't available).