I don't have any problems with the US spooks asking an EU spook for the data from a specific suspected Muslim terrorist. The EU spook would probably comply, due to sharing agreements that are already in place.
However, what the NSA does, is to simply harvest anything they want from anyone. I am not comfortable with that. And I don't believe an EU spook would set up a system enabling such universal access. If the EU spook can say the data was harvested outside the EU by the NSA, the EU spook has no problems. If the EU spook enables harvesting . . . we will see the EU spook in court.
Note that Snowden's revelations did not result in any legal action in the US, despite that the NSA is clearly violating the law. This decision by the EU court is the only legal action that I know of.