You reap what you sow Fred. Volunteering information to questions they have no legal right to ask is what YOU planted - extra hassle and long delays is what YOU got for doing so.
What I have done when asked what is in a package is politely tell the clerk to go fetch the branch postmaster because I insist on talking to them personally. I will not debate policy with a clerk, and I stand my ground. My only delay in shipping my package, if any (as most clerks will back down), will be waiting for the PM to come up to the counter. Be polite and professional with the PM, state the facts and don’t whine, and you may be pleasantly surprised how quickly you are accommodated. After all, you are a paying customer, paying for a service within their policies and not for a hassle. Either way I still file the complaint noting the clerks name and the PM’s as well if warranted. The USPS will not change unless we change it. After standing your ground a time of two you will be recognized by the clerks and will get service with a smile, and the only questions asked beyond the fragile/perishable chant if any will be about the weather.
You are not doing anything illegal or against USPS regulations and policies, and so have nothing to feel guilty about except letting a clerk push you around.
WA