Still, if one were to suggest that MWD may not give an absolute answer due to the laws around the world, if one takes a look specifically at the keylogger example, MWD specifically states:
"4. If you are convinced that nothing in your marriage will change unless and until your spouse is confronted with hard evidence about his/her behaviour, then you might consider purchasing a software product that takes "snapshots" of online activity for review later."
She very specifically suggests that as an option to any who feel that is the ONLY way. She also makes no disclaimer about the legal implications nor on what computer a person should or should not put the software. As printed, the publishers are well aware of the global distribution and the variations of laws within jurisdictions.
I suspect MWD is not at all vague about what she believes is and is not appropriate. I suspect that MWD's statement on snooping is very clear regarding gathering information and for what purpose.
MWD's two disclaimers on the above?
1) Be prepared for what you might find, it could be true and more than you were expecting or wanting to find.
2) The AP may not appreciate the intrusion of privacy and go so far as to use that as further justification, putting the BP back to square one.
Others may have differing opinions. The above is MWD's stated DB opinion.