It's an interesting one.
Rugby, as a sport is under huge pressure to minimise injuries, especially head injuries, and to be cynical, there are probably two approaches.
The first is to make changes to the game to improve safety.
The second is to be seen to make changes to improve safety.
The former benefits the players and presumably the sport, the latter benefits the organisation(s) in terms of legal liability.
I thought the red card was harsh live but I can understand why it was given. The player turned sideways so the referee pointed out that he had time to minimise the impact. There's a reasonable argument to be made that by turning as he did he made the situation worse.
Not for a second do I believe it was intentional but now in similar situations players will be more careful.
I'm not happy that it was rescinded, though. That sends a confusing message to referees for the future. "No ban but the card stands and we will look clarify the laws" would be fairer, I think.
The "no contact with the head" edict has made any team vulnerable, whether that be for a moment of madness, ineptitude or just sheer bad luck. Any team that isn't preparing for it (in terms of coaching players and devising plans for the temporary or permanent loss of a player) is going to suffer.
The focus here is to protect players. It is not on the entertainment value of the game. Insufficient player protection and the game won't last long, anyway.
A few random points.
The Irish player failed his HIA and could not return to the field. There's an unfairness there if the perpetrator was able to return.
In terms of cynicism and manipulating rules I believe Owen Farrell was encouraging the ref to send Johnny Sexton for a HIA. (That's not a criticism of Farrell nor England. That's what top competitors will do).
Most pundits would suggest that English discipline has been pretty poor during the tournament, perhaps to be expected with a new man in charge. There was an early red card in the Irish match last year too, though.
It is probably a good thing that this happened now (perhaps not so much for the English). It's controversial, has ignited a big debate with enough time to clarify everything before the World Cup.