Hi, Blair did not say that stops are always defensible.
(1) First, he said that there may be *some* circumstances （有些情况下）where stops are both legal and defensible.
(2) Then he said that if the stops were *solely* (i.e., *only*) motivated by race, then they are not defensible.
(3) Finally, between the quotes, the statement is that "if a police officer stopped a person only because of his/her race, then that would be an offense (i.e., a violation) under the law." This is the same statement as (2) above.