Vote for the USPS with your dollars; simply don’t buy from an on-line retailer who will not deliver by USPS.
You. Don’t. Need. It. That. Bad.
Yes, buying stamps funds the USPS, which, BTW, the Government is CONSTITUTIONALLY REQUIRED TO DO.
BUT THE OTHER HALF OF THE EQUATION is to NOT fund retailers who don’t ship by USPS and are thus actively working to destroy the USPS. Not to mention, if you happen to be a small retailer yourself, using USPS to ship, even if it’s a tad “inconvenient”.
IF you are actually serious about saving your Post Office, that is...