I've worked in many companies/teams that gave lip service to the truth and open/honest discussions, but it usually only took a few times ignoring these principles to kill any trust in the idea. Rebuilding that trust takes time and usually starts small -- it requires demonstrations that persons with power in the company will do their best to protect against repercussions for objective, good faith open reporting (the truth). This will take awhile from my experience, and in many cases there is a need to define 'good faith' a bit more, else truth sessions typically end up as emotionally charged finger pointing sessions.

It's possible to do all of this, and not even hard, it just means that those who are asked to lead will need likely need to deal with some emotionally charged arguments for a time if/when someone uses the same policy for emotional venting. Nothing wrong with a bit of venting, leaders should be able to handle this gracefully also, but my experience is a lot of leaders are not trained or prepared on how to handle such situations, and the tendency is to rely on the authority of their title rather than address the concerns directly.

Basically, there isn't much to it, it's just a rather awkward path that is best started in smaller groups, establish clear and unambiguous boundaries [0] for such a culture, and provide new reasons for people to trust in _this_ system which has likely failed them historically.

0 - I wouldn't read too much into what the boundaries should be, it's something that is dependent on the people you work with. For a team I was asked to lead, it was set early on that openness and objective discussion were essential -- if a project or situation turned sour, it was established that the important thing was to know and understand why it happened, not to punish, and that meant giving freedom to the team to make mistakes and that while we would review and correct mistakes, the team would also be protected from those "out for blood" over the mistake. It was probably 2 years of ugly arguments with other teams who wanted a scapegoat, but the end result was the team I was asked to lead grew very fast professionally and we got very good at self-correcting and owning mistakes when they happened. Boundaries for the team were that "sometimes" there are going to issues we must handle with a few "we really must avoid messing up here" clauses included -- being extremely judicious with the use of such clauses and ensuring they were truly the exception and not the standard helped retain the sense of importance for such clauses while maintaining the team's freedom to handle projects in the "best" way.