This is cheap and will improve our standing in the world as the great benefactor of charity and commerce.
I shall repeat myself - do you have evidence, or is this merely speculation?
Let me revert the question, have you any proof this will not help our standing?
No, I don't have any proof, but I'm not the one making claims - but you are the one claiming that there will be benefits. Therefore, the burden of proof is upon you.
Now, if you'd like my personal, non-scientific opinion, based only on experience, I would say this would have very little effect - even if the effect was positive, it probably wouldn't be cost-effective. When I see 'Made in China', 'Made in Taiwan', 'Made in Mexico' or any other such 'Made in X' label on a product, I don't really give a rat's ass. I'm not grateful to China, Taiwan, or Mexico - someone else would manufacture it. I would imagine the vast majority of people are the same - we want stuff, we don't care where it came from. As far as charity, I know tons of stuff is sent to Iraq and handed out by American troops - like a flag would help there - yet there are still insurgents and whatnot.
Furthermore, why print this on the boxes? As a consumer, I rarely see the box or package a product was shipped in, I see the final product on a shelf, only in the pretty packaging that catches my eye to buy it. So, thusly it seems the only people who will be seeing the flag are those who are involved in shipping - and they are working, they aren't thinking about gratitude, they are just thinking about getting done and going home to relax.