Well there are four primary questions that need answering before we start testing incoming passengers for SARS:
Is there even a SARS test?
Not really. The U.S. CDC can confirm it if you give them two weeks for testing. Various other tests can be done much quicker, but they have a high false negative rate.
How long does the test take? Too long to wait.
What's the incubation period before the test will come up positive? The false negative rate is high.
Where are we going to put these people during the incubation and testing period? Nowhere. If we let them come, we cannot confine them once they are here.
Everybody acts like it's a no-brainer to test for SARS but frankly it's a no-brainer to NOT test.
The only practical test is to screen for obviously sick people. This will not catch all cases, but it could catch enough to slow its spread. It is still thought that the most contagious time is when symptoms are present.
Even if we cannot keep it out, it is worthwhile to buy time. If the extra time we buy allows us to develop a practical and reliable test, for instance, we will be much better able to contain this. Likewise, it is still possible that this will turn out to be seasonal, or will burn itself out. In other words, slowing down the spread is worth doing even if we cannot keep it out in the end.