Thinking about it, that does make sense. Are you thinking in terms of "we are all one" is basically empathizing with others only because they have something in common with YOU, so you're still using yourself as a "bar" for what is acceptable? Which would mean if they were truly different, you'd not be so accepting or empathetic. I suppose it's just an expanded version of "hey we're all Americans at the end of the day", which isn't that different from "Hey we're both made of atoms" or "Hey we are part of the same universe" - anything you use is still somehow trying to tie yourself to someone else as a reason to be cool.
In that case I'm not sure why we need to share something in common, whatever it may be, to try to understand others or care about them. In other words, I don't think that's necessary - I just never thought of it in that way.
As for the purpose - well, again, I was thinking along the lines of experiences in general, we're all atoms, we're all adding to the knowledge of The One so to speak. But it kinda goes back to your other point - even if so, so what? What can we even do with that knowledge, why is that so important to acknowledge in the first place? It's like we always look for some commonality, no matter how vague or fundamental, before "it's cool"... weird!