The quoted statement by Deotis Roberts is based on a false assumption.  "[A]ll life is of equal value" is not true.  

For example, we usually hold that human life is more valuable than other life (vegetarians may disagree, but they would probably hit a squirrel rather than swerve off the road).  Even if Roberts only referred to human life, the assumption is questionable.  We triage patients.  Adventists take the position that abortion to preserve the life of a mother is justified.  Society applies capital punishment.  We "pull the plug" on the terminally ill.  We award scholarships to smarter/harder-working students.  Secret Service put their bodies between a shooter and the president.

In short, most humans rationally do NOT think all life is of equal value.  With respect to the article, the question in a policeman's mind is whether a criminal suspect's life is worth more than their own or that of others nearby.  It is rational for them to answer "no".