Rick O'Shea (English language commentator on S4C) made the point that the IRB doesn't allow referees discretion on 'spear tackles'.

From the IRB Memorandum (8 June 2009):
"At a subsequent IRB High Performance Referee Seminar at Lensbury referees were advised that for these types of tackles they were to start at red card as a sanction and work backwards."
...
...

"To summarise, the possible scenarios when a tackler horizontally lifts a player off the ground:

The player is lifted and then forced or "speared" into the ground. A red card should be issued for this type of tackle.

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.
Referees and Citing Commissioners should not make their decisions based on what they consider was the intention of the offending player. Their decision should be based on an objective assessment (as per Law 10.4 (e)) of the circumstances of the tackle."