I've never worried about being sued myself (not that kind of guy) but the logic is pretty much straight forward to me.
Good samaritan laws protect people in most situations where they try to render aid, in good faith, and to the level of their training whether the victim survives or not. Basically, if you act as a reasonable person would, you're safe. The question is "Is punching/kneeing someone in the gut/chest something you are trained to do or reasonable" under the circumstances.
There are two conflicting mechanisms of injury at play in a bolting diver (when the origin of the panic is unknown). Drowning and DCI. Of the two, which is more likely to be immediately fatal - drowning. What remedy is offered - strike to the gut/chest with the intention to force the diver to exhale. Enhancing the chance of an immediately fatal drowning to prevent a less immediate DCI is not acting in good faith, reasonable nor is it acting to the level of ones training because no one trains divers to do this.
Your best defense would be that someone on scubaboard told you to - good luck with that.
I can't remember if it was the Buddha or Hypocrates who said "Whenever possible help others, but if you cannot help, do no harm."
Humm... maybe it was both.