If you want to get a red line, you need to use red ink. If you use blue ink, you'll get blue lines. And I can draw you cat. (I'm no artist, but I can give it a try.) But it it won't be a line anymore. A line and a cat: those are two different things.
That's a proxy. It's right in the name.
Yes, it's proxy. If there are no serious privacy concerns, I think it's fine to use it (if there is no other option).
I'll simplify:
If you want to get a red line, you need to use red ink. If you use blue ink, you'll get blue lines. And I can draw you cat. (I'm no artist, but I can give it a try.) But it it won't be a line anymore. A line and a cat: those are two different things.