So then are we trying to reduce numbers of head collisions without regard for the severity of the ones we're potentially going to see more of as a result and which are justifiable as "rugby incidents"?

Jammy you're obviously quite well read on this - how do you prevent a pick and go a couple of meters out from the line if you have to go for the legs?

the French also proposed a "partner law change" that would regulate the actions by ball carrier.  That is, they said that the ball carrier would not be permitted to drop their height into contact, or to bend down and lead with the head.  In their words, the "defender must be able to tackle the ball carrier and so have access to his pelvis".

More concerningly, and relevant to this story, was the negotiation about what to do when the ball carrier is low in contact, leading with their head.  This often happens near try-lines, and also in so-called pick and go situations.  Even in the wider elite game, this issue came up a lot.  People would protest harsher sanctions, saying "It is impossible for the tackler to avoid head contact if the ball carrier is in a pick and go move".

The thing is, if you watched rugby any time between 2010 and 2017, long before the high tackle and head contact focus came along, you'd see 30 to 50 of these situations every match, and they were never an issue.  Almost always, the ball carrier would duck down, lead with their head into the tackler, who typically stayed upright and 'soaked' the player.  This situation would produce head contact, so strictly speaking, is a 'high tackle', but they are never sanctioned, and nor should they be. The involve a bent ball carrier against an upright tackler, and head contact from the ball carrier's head to the tackler's torso or arms, in a wrap tackle.

We know that the risk from these is low, and so there's no need, even from a risk perspective, to act on these.  They were never penalised, not before 2017, not since, but they became the focal point of dispute.  In the attempts to navigate this issue, I believe a perception was created that the tackler had to be lower than the ball carrier, no matter what.

This was, in my opinion, an imagined or exaggerated problem, but it became crucial, because the response by coaches and players to lowering tackle height was to forget that these ball carrier induced head impacts have always been quite common, and instead, tacklers began reacting to the ball carrier in what became a 'race to the ground' while still trying to 'hit' the opponent in a dominant tackle.  As a result, a lot of dangerous tackles were created where tackles were trying to contact ball carriers low, the result being that two heads were still sharing airspace, but with both players charging into each other low to the ground.  An image of elephant bulls fighting for territory comes to mind.

It needn't have been like this.  A tackler who remains upright and "high" could safely and legally execute a tackle on a bent ball carrier, even with the lower tackle height trial, but this happened less and less often, replaced instead by something we can predict would increase risk.

The French solution, as I mention above, was to stop the ball carrier from dropping into contact by creating a law for that player too.   And it worked.