Earlier quoted context omitted.
I've had this and private offices... what happens is that difficult conversations can't take place except outside of the office (unless there is another space to go). Need to have a 1-1? Everyone else hears it. No meta conversations can take place unless someone is willing to go out for some coffee. The team banter ends up being trivial, and can be incredibly distracting if you need to buckle down to get something do…
Your office doesn't have a single shared meeting room? Most places I've seen with open offices have some sort of meeting rooms to use for private conversations. How do you have a client call or anything of that matter?
Yes, people do use it for those conversations, but you have to walk past all the business/marketing/sales people and your boss(s). Outside the office is a place to confide - where an "official" meeting or neutral meeting room is a place that puts everyone on the defensive, more so than anywhere else.
The idea put forth by Mark Cuban that "there should be no secrets at a startup" is extremely unfounded in my opinion - unpopular opinions or contrary positions frequently only flow in privacy as to not cause embarrassment or hostility.