The "behind closed doors" concern is mostly fake. "Secrecy" is a story line that tests well with folks who don't know how policy gets made in general. For example, the PPACA (aka Obamacare) and Dodd-Frank bills were extensively negotiated in private before being offered on the House and Senate floors for votes. I don't recall much complaining about secrecy then (edit: I mean from Democrats like Senator Warren).
Generally speaking, people object to private negotiations only if they object to the substance of the negotiations.