Either..

(1) The picture causes more harm to the child in every *inappropriate viewing of it, because that child will know that people are obtaining sexual gratification from something they did not want to do (especially if they have been through therapy) or be recorded.

(2) Viewing the pictures **causes offenders to act out

* - Inappropriate as opposed to appropriate, apparently making it okay for police, or anyone to view these pictures (the same act - ie Viewing) for "legal purposes" - apparently that is not harmful in any way.

** - They assume this falsely because they have made "many studies" of these offenders, and found that at least some of these offenders have child porn. - rather than having any evidence of the number of cp collectors there are to those who act out - which would be infinitly more useful to prove this fact or not