Standing up for your principles is not making a mountain out of a molehill. Any good friends should understand and accept that. There is far too much pressure to do what is superficially polite without any consideration for principle, in my opinion.
Quite apart from anything else, it's presumptive, not to say a bit rude, to expect an automatic present anyway.
A better approach, I feel, is to say that IF anyone wants to give a present, p,ease could they make a donation to THEIR favourite charity. Then everyone is happy and no untoward pressure is put on anyone either.