for the tl:dr group:
"The problem is that changing these rules imply making a new hard fork. So ethereum is saying [ethereum classic] should do it. And the classic guys are saying that [ethereum creator] Vitalik [Buterin] should have considered it on their hard fork, so they should do it."
I think the entire article is worth reading as it covers a lot of specifics including problems at various cryptocurrency exchanges. Here's the link
http://www.coindesk.com/rise-replay-attacks-ethereum-divide/