I suspect that fundamentally, the FDA do not like stem cells...

I suspect that fundamentally, the FDA do not like stem cells because they are unable to fully understand them because they are too complex.

The method of action and the potency are too variable / uncertain for their liking.

The fact that it is more effective than any other option (wrt ARDS in child SR GvHD) and is safe is simply not satisfactory. I think their mindset is a very traditional form of science where the cause and effect is very simply and clear without any ambiguity at all.

But stem cells are cellular products that are so complex that we will probably never fully understand them. That doesn't mean that can be used for our benefit.

Nassim Taleb refers to such people as IYI - intelligent but idiots. They have great models (like economists) to explain phenomena but fail to accept that life is complex and there is always uncertainty and ambiguity in in some realms - most particularly the human body.

They can see x % of patients benefit and that this is higher than any other option but they need to know all they why's and wherefore's and this may not be possible.

Requesting double blind test for ARDS in SR GvHD children is a reprehensible and a cold act of a IYI.

This feels like a slap in the face to the professionals who treat the children.