I think this is a bit of a storm in a teacup, from the 7th ed. rules:
So opposed rolls are quite voluntary and if not liked ignore on the whole?
How I run the "sneaking" past a guard scenario.
Is the guard a "mook" then a successful investigator roll always succeeds, but this may be very hard due to lighting, skill or position.
Is the guard a "named character" then I roll for the NPC and look for the level of success. Each level of success will be a penalty dice for the investigator.
Good roleplaying will always trump mechanics in my opinion, and even in combat this applies.