Even if I knew for a fact the NSA would get my fingerprint from my iPhone it would still be worth the convenience of having that fingerprint auth. I can legitimately stop putting in a pass code all the time and still have my phone be secure against random people using it, strangers finding it and getting access to my email, etc.

I would prefer the NSA not have my prints but virtually every other piece of data they collect is more likely to be used against me.