There are reasons why people keep secrets. Exposing more of yourself allows better cooperation, but also better attacks.
A partial solution is to expose yourself to your friends, and maybe expose the harmless information to the world, but keep everything else secret. But you need to consider that someone who is friendly (or seems to be friendly) today, may not be friendly tomorrow.
So, the situation with irreversibility is complicated. On one hand, yes, if someone refuses to make a record of their words, you should suspect that they are planning to deny them at some moment in future. (When your boss tells you to do something that seems fishy, but refuses to write it in e-mail or to reply to your e-mail asking for clarification or confirmation, you might consider contacting a lawyer.) A hypothetical perfectly open person would be willing to put everything in writing and post it online.
On the other hand, if there is a good reason to avoid making things public (e.g. to avoid retaliation by a third party), I would expect people to be more open when speaking privately, and more reluctant to write it down, or at least to write non-specifically. Because the alternatives to speaking openly include not just being silent, but also speaking vaguely, or telling a part of the story but avoiding another. So if a good friend writes something vague, I would expect them to be more open if I ask them privately.