"If someday the court rules those subpoenas as unconstitutional too, then I will change my opinion to match yours."
Do you agree with every decision the SC hands down? Do you agree that abortion is a constitutional right and that we should limit political speech?
"Do you agree with every decision the SC hands down?"
I'm saying administrative subpoenas are legal to investigate drug trafficking, insider trading, health care fraud, and violations of OSHA. I could turn this around and say "are you saying you believe terrorists are in a more preffered and acceptable class than OSHA violators?" It's a legal tool, so use it. Unless (or until) all subpoenas of this type are made illegal I see no reason to not use them.