Your response, whilst emotive and impassioned, doesn't really address what I said, does it?
Whilst we can ignore the first paragraph, as it in no way relates to either the content or inference of my post, I suspect you might find clarification helpful.
At no point did I suggest the OP is being naive; indeed, she may be absolutely spot on about an affair, but I think I made it pretty clear in the opening line that that's not the point I was making...
Which segues neatly to your second paragraph.
You mention that you and your DH allow each other to check your phones all the time. Whilst this practice may work for you personally, it is unusual. I'd gently suggest that personal privacy or, at least, a sense of the same, is absolutely sacred to most human beings. A desire for, and expectation of, privacy doesn't automatically equate to an admission of guilt, despite authoritarian regimes the world over really wanting it to ("If you have nothing to hide, you have nothing to fear" is, of course, a logical fallacy).
In respect of this particular thread, I repeat that I firmly believe everybody has the right to expect personal privacy and that "snooping" (the OP's word, not mine) on another person's device is an invasion of that privacy.