If you answer "yes" to the "are you carrying anything for anybody else" question then you will be denied boarding. So the question might as well be worded instead "Do you want to be denied carriage, not get to see your family, and lose the fare you have paid as it is nonrefundable ? Answer yes or no".
I've done this a couple of times and was asked to explain the situation. In one case (travelling on a US airline) colleagues had given me envelopes containing documents they wanted hand delivered to one of our other offices. They looked at the envelope, but didn't open it (it was unsealed) and then went back to checking me in. In another case I had packed in my hold luggage something my wife wanted me to post to one of her British relatives since I was going to London anyway. Again they appeared to be completely unconcerned after I explained and did not want me to open my bag before they sent it down the chute.
So I don't believe it SOP to deny honest travellers when the answer to this question is "Yes"