Meh I'm fine with the Crighton one TBH. I don't think there was that much force in it and he did slip significantly. Crighton didn't come out of the line Suali'i style.
Having said that, I completely get the inconsistency issue and that less has been binned and charged etc
He may have slipped into it, but Crichton used the top of his shoulder which collected him in the head. I mean it was only a couple of years ago a Dragons player was charged and (IIRC) suspended for a similar type hit on James Tedesco. I can remember the outcry from some about how Teddy was always "falling into" tackles, and that and similar incidence were on him.
At the end of the day, Crichton used an illegal action, namely a shoulder charge, to affect the tackle. It was accidental to some extent, but considering the conditions, you have to take into account that using a "tackling technique" outlawed in the rules may have unintended consequences. That's why I agree with Nick, Crichton should have been charged. Its inconsistency by the MRC when you look at matters holistically.