Saying the NSA doesn't care if you've smoked weed is like saying the telephone doesn't care if you've smoked weed. It's technically true, but you can still get arrested for things you say over the phone. Same with the NSA, where they don't actually enforce the laws themselves, they're just a data provider for everyone else. And even if no one cares now, when the data is stored indefinitely, things you're doing/saying now that are completely innocuous could be used against you years or even decades in the future. Ex post facto won't stop the government from banning you from getting on a plane, getting a passport, taking out a bank loan, etc.

I would be somewhat concerned that NSA records could be used in employment verification (with NSA, or in government, or in general) in the future. Maybe "smoked pot" would not be a disqualifier, but what if a 22yo NSA candidate did coke at a party or something.