The iRB directive about red-carding pretty much anything near a spear tackle seems extreme. Even if we uphold the letter of that law, there is always going to be debate over the classification of Warburton's tackle between these two options:
"-The lifted player is dropped to the ground from a height with no regard to the
player’s safety. A red card should be issued for this type of tackle.
-For all other types of dangerous lifting tackles, it may be considered a penalty
or yellow card is sufficient"
Warburton seemed to let go of Clerc, but he brought him most of the way down, and had he not released I feel would have put unnecessary force driving through Clerc's upper-back/neck. It seemed to be an attempt to pull out. I would definitely have classed this as 'all other types of dangerous lifting tackles' and given a yellow card.
We also have to question whether an Irish referee with French connection was the right call for this match? You would have Nigel Owens refereeing a Welsh match at a World Cup, JMO .