Instead of using this approach, why not use the Specification pattern to validate your data... Doesn't have to be from a POST, data could be from another source - anything in fact where rules apply.
It frightens me that in this day and age that this pattern is often not implemented by many developers, yet I've been using it for the past 3 odd years now.
Lack of education I feel but I don't want to go off topic as it's not my blog; the point mentioned by Lorna to me is obvious but again often forgotten :(
Lack of logic I feel (there I go again, having another moan...).