Terrorism is beyond the scope of Islam alone.
Could be. However, we haven't had much trouble with terrorists who are not Muslim. That being true we should probably concentrate on that genre of terrorist.
The IRS attack was a white guy angry at taxes, religion had nothing to do with it.
Right. But that was an act of anger by a single person not part of a larger plan hatched and raised by a group dedicated to the destruction of the IRS. So, back to concentrating on Muslim terrorists who are part of a larger group that plans and carries out terror missions against us and others.
The sectarian violence that has been spreading in this country? Almost exclusively Christian.
You'll have to point me at terror events Christians engaged in in the US in the name of God. Also, you'll need to point me at which US based Christian terror orgs have sent their agents to conduct these terror attacks.
And what of all the Chinese and White Muslims (the majority)?
What of them? Most terrorists have been Arab Muslims. Certainly not all but most. Back to using profiling as a sifting tool. Back to realizing outliers are outliers. That they exist doesn't mean we should give up a tool that helps pick the low hanging fruit.
What good is profiling Arabs when they account for just 20% of Islam? What about the other 80%?
See above. The disparate rate of Muslim terrorists makes including "Arab" on a profile very useful.
For every terrorist that is caught thanks to profiling, how many will be unjustly detained? How many will not be profiled? Jihad Jane isn't an anomaly, the Russians can tell you as much.
I don't know. How many dead people are you willing to accept in order not to upset an innocent person who fits the profile sufficiently to be detained to determine if more scrutiny would be advisable?