The thing is nobody saw that though (unless they let their bias convince them), all we saw were soldiers wearing generic soviet gear, they could have been from anywhere as Ukraine use that gear too so it would have made sense that separatists would have sourced their gear locally.
Seeing that and denying it alone proved they were Russian soldiers is what most people would call keeping an open mind.
Because that's kind of the definition of keeping an open mind, being open to all possibilities until one is actually proven!
They have been proven. You just won't accept the proof. So as I say, get yourself over there and see for yourself.