Personally I think that this, as with most ancillary laws, merely encourages less disciplined thinking on behalf of those who enforce it. One law isn't practised carefully and accurately enough, so an additional one is introduced as a kind of buffer, then that isn't applied properly, so another is added, and so on and so on. What it ultimately comes down to, surely, is the failings of refs being excused by an excess of rules. Train refs better and you'll need fewer rules, not more of them.
A ref needs a much sharper sense of when to, and when not to, show a yellow or red card - not an even fuzzier sense. The amount of deliberation required to judge which card is most deserved would be better suited to post-match committee meetings than a ref in the heat of the action. For one thing, a green card seems to sit there between a yellow and red like a cuckoo in the nest. It doesn't so much complement the other two as flap wildly about around them. There are lots of potential offences that could get all three cards, or one or two of them, depending, seemingly, on the whim of a particular referee. And how it would fit with VAR, which is 'supposed' to clarify and simplify the existing procedure, god only knows.
I think what's needed are fewer rules but more grown-up conversations, and warnings, from a ref to the players.
