Actually, by law the OP can (usually) be handball but there may be times that it is not. They have not specified when those times are and that is when you get your inconsistency.
Again comparing it to a physical foul which is also a subjective decision we also have inconsistencies but a lot less. That because the laws have better definitions. They are not precise but they are better than the ones for HB.
On the other hand, there's a fundamental philosophical separation between physical fouls and handball.
With fouls, the line between careless and reckless doesn't mean much in terms of whether a free kick is given - the only real difference is whether a card is justifiable or required. And even then, you can say that ITOOTR it was one or the other and therefore the card was required/possible/not required. The referee has a "get out of jail free" card built in.
With handball however, the distinction for comparable offences doesn't involve cards, but between a free kick and playing on.
Especially when it's a fairly black-and-white question, "did the ball touch the hand/arm, yes or no?" that forms the majority of the decision, and a variety of refereeing cultures hold different views in what should and shouldn't be a handball offence (for example, some posters here still don't accept that something can be handball without also being deliberate, as shown by a repeated emphasis on using solely that criteria in threads about handball, regardless of what the laws say) then the result is a black-and-white dispute.
If the laws just said "it
is also a handball offence when ..." instead of the "usually is" nonsense, and similarly went "it
is not an offence ..." for the "not usually" stuff, yes, we would lose a few corner cases where we don't really want to be giving handball generally, but we would be saving a lot more events where we overwhelmingly agree we should be giving handball, and avoiding a huge amount of reliance on idiosyncratic beliefs of what the game should be (instead of what the collective and official views are).
)
I've given up caring and will now just ignore any / all handball posts as even VAR seems at odds with LotG wording 
