It has bothered me that sometimes, with regard to goyim something is not really wrong according to the torah, like we don’t have to return an aveidah to a nochri, but because of chilul/kiddush Hashem we do it. If it’s really not wrong, why are we “polishing” the Torah in front of the goyim and if really this is the right thing why didn’t the Torah command it?
The Shulchan Aruch CH: M 266-1 writes, “The lost item of a gentile is permitted to keep… and one who returns it to him did an aveiro, because he is strengthening the hands of sinners. However if he returns it in order to make a Kiddush Hashem, so that Jews should look good, it is commendable.” We see from this that it is actually wrong.
There is another reason given, in the Sm”a (ibid 2), that by returning the lost item to the goy we see that he reason that he is doing the mitzvah of hashovas aveida is not because H-shem commanded us to do so, rather because of his own feelings. That is an incorrect thing to do.
However if the reason we are returning it, is to glorify Hashem’s name, then it a commendable thing to do. Not because it is good to return his object to him, but because the mitzvah of Kiddush Hashem is so great.
I would also recommend that you see the following link http://dinonline.org/2017/02/28/mitzvos-bein-adam-lachaveiro-to-non-jews/ that discusses mitzvos bein adom lechaveiro that we don’t do to gentiles.