Does anyone know the history of the requirement that some vehicles in
California obtain their smog certificates from a test-only smog
center?

The California DMV website is silent on the matter, but from what I've
read the reasoning behind the policy is that the "primary obligation
[of a test-only center] is to conduct a fair and unbiased smog
test."  (http://www.smogtips.com/test_only.cfm)

This reasoning appears illogical.  If California is worried about
reducing pollution, it should send owners to test centers capable of
repairing vehicles.  Those stations would be likely to err on the side
of ruling that a vehicle does not meet emissions standards, because
such a ruling allows them to charge the owner of the vehicle for the
repairs.

By contrast, if California's concern is to protect vehicle owners from
unscrupulous testers inclined to finding that a vehicle does not meet
emissions standards, the requirement does not fully address the
problem because not everyone is required to use a test-only center.
Moreover, if the purpose is to protect vehicle owners, the choice of
which testing-center to use should rest with the owner; the state
should simply recommend a test-only center.

Am I missing something?

Thanks,
Andrew