The killing example still bites you because the intent to kill, knowing & abetting, etc still matters, regardless of method to do so. It's not just the murder, but also everything around the murder that gets swept into it.
It seems to me data collection is illegal, so TSA doesnt do it directly -- the problem is that TSA intends to collect, and knowingly (and provably?) works around it, but is not being punished for it.
This is not really true. The TSA does not intend to collect, but to obtain an "ok person", "not-ok person" stamp. Then they decide with the info they gathered in the conversation with the person in question. They are not obtaining the data and have no intention of doing so. Yet a stamp like "criminal activity in the past" would be a questionable one. I don't know how they stamp the person.
Nevertheless I think they are doing a bad thing, because you can rest assured that this collected data won't get deleted, possibly even sold to 3rd parties.
It seems to me data collection is illegal, so TSA doesnt do it directly -- the problem is that TSA intends to collect, and knowingly (and provably?) works around it, but is not being punished for it.