Lots of people, but the people that matter in the negotiation are the Republic of Ireland who will not accept it, full stop. And that means the EU is not going to negotiate a deal that doesn't include the backstop. The EU throwing Ireland under the bus would severely damage its credibility with its smaller member nations. The EU does a lot of things by consensus and voluntarily throwing RoI into economic and political turmoil to appease a country that is trying to leave the EU is a nonstarter.

There's also the Good Friday Agreement, which brought peace to Northern Ireland. A hard border would easily be seen as a betrayal of it and could plausibly cause it to collapse.

The whole thing is just an impossible trilemma. Can't have a border on the island, because RoI will not let the EU sign that deal. Can't have one in the ocean, because the Tories need the DUP votes in Parliament (they don't have a majority, and the government will fall if the DUP pulls out). Can't have a backstop because it could mean a permanent half-in half-out twilight where the UK stays in the customs union forever and hard Brexit parliamentarians can't swallow that. Three totally incompatible red lines.

https://en.wikipedia.org/wiki/Irish_border_question

The default, if no deal is signed, is a hard border on the island. Which is bad, but not obviously that much worse for the RoI than a deal with a hard border. So the RoI won't settle for a deal without a backstop.