Hot topic nowadays. I have also given it a lot of thought but couldn't come to any conclusion.
It's true, living in SF/NYC and India, you will have a significant difference in monthly expenditures. But does it make sense to pay differently to persons who bring the same value to the company just because they are living in different locations?
IMO if you are a fully remote company, it shouldn't make any difference. People can choose to work from wherever they are and should get paid equally. If you have an office and hire a remote worker, it would make sense if you are paying lower to remote workers working from countries with lower wages.