“Good manners cost nowt, but can put many a pahnd in tha pocket.” So goes an old northern saying, but I’m glad to say that even when I first heard it spoken, when I was a little boy in Yorkshire, I thought its reasoning was a little twisted towards self-interest.
As a proud Yorkshireman I can honestly say that I thought the expression began and ended with “Good manners cost nowt”. Maybe those is learnt it from shared your concerns about the remainder of the saying.
Over the years I’ve often heard people say “It’s when I’m nice to you you need to worry” which does tend to support your argument about good manners being used as a carapace to keep out those we don’t know or trust.
Personally, my view on manners is similar to my view on dressing ‘appropriately’. Everyone has the right to dress (or behave) as they want, but they then they must accept that others have the right to respond to that as they want. Dress or behave like a yob and be expected to be treated like one.
Consideration is the precursor to indifference, I have considered the science behind Global Warming but i have found that i am totally indifferent to the fact, I suppose i am a bit like the other six billion of my species!