The summary is that we don't know enough about terahertz radiation to draw any solid conclusions yet, and there is at least one reputable source pondering, "How Terahertz Waves Tear Apart DNA": http://www.technologyreview.com/view/416066/how-terahertz-wa...
Do you know how much power is emitted by the terahertz-wave scanner as two antennas are swept across your mid-section in close proximity?
Here are some responses to your other points about mm-wave:
Passive mm-wave scanners do not produce radiation
Passive mm-wave scanners are not used in airports and not relevant to this discussion.
You'll pick up far more radiation on the flight itself at a fairly low 5 mrem (50 µSv)
Also, irrelevant as the xray body scanners have largely been removed from US airports due to their safety concerns. The EU has also banned the use of those scanners. The study that you cite is for radiation applied to the entire body mass, while the xray body scanners applied all of the ionizing radiation only to the outer layer of the body (skin + some bones + male reproductive organs + brain).