If you are living in a country that is not save and free from politically motivated prosecution or other dangerous pursuits, all activities, messages and so on, that are critical of that country could be seen as dangerous to said system and therefore illegal. So making them public puts you in great danger. By “public” I don’t mean publicly available, but readable for state actors.

If you are living in a currently safe system, the internet does not forget things. So when it flips to an unsafe country, all your previously save thoughts, messages and so on are now illegal and are already out in the net. That puts you in great danger if you ever in your past had interactions which are now seen as illegal. And you can never know which topics could be illegal or dangerous by then. 

Another example would be traveling to unsafe states that you were ever critical of. 

All of those (and possibly more) scenarios are dangerous for you as the actor, but for any family member of yours in the future (or past) as well. 

So would it not always be in your interest to hide as much as possible, not just depending on your current situation or the assumed threat level? I have a hard time wrapping my head around statements like securing oneself depending on one’s threat level.