If someone gave me porn, and I disapproved of porn, should I give that to someone else? Giving someone a gift implies that you yourself approve of whatever it is you are giving. A better solution would be to give it to a crisis center, a homeless shelter, or an orphanage of some sort.
It doesn't hurt to tell the relatives that you don't shop there, but do enjoy shopping at wherever you feel is more PC. Just don't lecture them on their choices.
I regularly am given cards for a chain coffee store. I don't drink coffee. I do regift those, because I am not morally opposed to coffee.