Hello all,
I think that "what would have happened if the offender was not there" is not as crazy as it sounds. First, we have to look at the alternative methods of assessment. If they try to evaluate whether, had the offending player taken a legal option, the try would have been prevented, is misguided. That is the question the offending player should ask himself before committing the infraction.
If the act of foul play is committed in a situation like this weekend's (i.e. in the in-goal, with a possible try opportunity), and the referees think that, had the player taken the legal option, then a try could have been avoided with reasonable probability (I'll come back to what "reasonable" should be IMO), then why did the player infringe then?
This takes us back to "reasonable probability": it is not 50%. We do not need even to know the number, and the TMO does not need to make any calculations or estimations. If the player chose to infringe, it means that he evaluated the probability of a try high enough, and that the only way of decreasing that probability significantly was an act of foul play. Therefore, penalty try and yellow card is correct.
Now, obviously, a player in such a situation will not engage in a cost-benefit analysis of the different alternatives, but foul play should not even be considered an option by players.
The only relevant question for the TMO last weekend was, then, whether the act was deliberate or not. Arguable, as pretty much any human decision.