FINRA recently ruled that ETNs (the one I care about is VXX) are no longer eligible for portfolio margining. I am not sure I understand the logic behind a blanket ruling like that. I understand that it may be desirable to prevent people from buying at a 1:6 or 1:7 leverage an ETN stock that can go belly up due to the parent's troubles, but as far as option risks and hedges working together in a portfolio margin account, I don't see what the fuss is about. Can somebody play FINRA's advocate please? It's not that we can do anything about it, but I/we may emerge wiser from the exercise.