What is acceptable (even legal) today may not be tomorrow, or in X years (10, 15, or more)..
If we allow all our private conversations and messages to be permanently archived (and you know they will be, disk space is effectively infinite), who is to say that wouldn't be used against us in the future when laws, or even social standards, have drastically changed?
https://duckduckgo.com/?t=ffab&q=facebook+police+abortion
It's the first like 4 links right now
How much do you want to bet states like Texas or Florida will use government surveillance to prosecute folks seeking medical care?
I give it a month before we hear about someone being charged with some form of conspiracy to leave the state before their poor kids are taken. "Exhibit A will show the defendants intent to move their children across state lines..."