Something I've yet to see in any complaints about screening is what the US CBP is wanting to see on a phone or other device when folks are being stopped. Again, there has to be a reason for them to ask - they are NOT allowed to just scroll through the contents of a phone or other device to see what's on it just for the heck of it - they will be looking for specific things.
With all due respect - and you seem like a friendly guy - this is just not true in all cases. There are reports, covered by legal websites and authorities, of devices getting seized. We also are hearing stories lately of people being detained at airports - sometimes without cause legally - and it's quite probable they get their devices seized. What you are writing about here are your experiences and what most people will experience - though even this is stretching it with a touch of generosity.
For foreign travelers entering the US - something that is always asked is length of stay, return ticket and lodging info, if you need a VISA to enter - what kind. Those are the basic things they will ALWAYS want to know and you should ALWAYS be prepared to give. Pretty sure that applies to entering any country.
TSA's scope only covers ensuring travel safety meaning they have no rights to actually examine what is stored on an electronic device as part of regular screening.
TSA has engaged in very intrusive and questionable behaviors far removed from promoting public safety. All you are doing is repeating government talking points - and again I mean no offense, as you seem respectful. TSA agents have been known at times to engage in theft. Much of their protocol, not always followed by individual agents, is arguably not serving the public in promoting safety. I understand that airports need to be secured, so I won't be an ass here and say they serve absolutely no purpose, but I'll go out on a limb and guess they engage in plenty of security theater.