I'm really surprised by both the number and the type of responses I get for my desire for an ecologically- and socially-responsible ring. They've ranged from "that's so cool!" to "this is your insurance from your husband! You should get something that you can always sell if you need money!"
I mean, wedding rings are a personal decision, so I was surprised to hear so many people weighing in. I'm still doing research on platinum, but it looks like metals mining is a messy business. Among the controversies out there are a Canadian mining firm that's trying to displace farmers in Nigeria to mine platinum. Thankfully, more and more organizations are springing up to ensure that metals for jewelry come from recycled sources, or are mined with sensitivity to the local community, including rehabilitating the environment afterwards.
So, if it is diamonds that you must have, here's another resource:
Brilliant Earth - fair trade comes to jewelry.