I agree completely, if we are talking about you, me or anyone else who has the other three so deeply ingrained in habituation that they OBEY them on a subconscious level.
However as most of the comments reflect how often the second is neglected and I will also say that the other two are not observed. I think it is important to ingrain the first. If i didn't believe the first it would, why would it be SO important to do the rest.
Your question illustrates my point.
The first "rule" sets people up to believe that the following three rules (the important ones) only apply to handling loaded guns.
Trying to convince people that their gun is loaded is not the answer. Teach them, rather, that unloaded guns are simply not an exception, not an excuse to ignore the 3 actual safe gun handling rules.
Teach them that all guns are always guns and should be handled as if they were guns. This loaded/unloaded nonsense is dangerous.