Usually, the more relaxed law on pornography is a result of general sexual liberation of the society and, consequently, there is also higher avaibality of real "non video" adult partners. So, thoretically, the porn could intensify lust, but bigger pool of available real-life adult partners can counter the effect. Some abusers, which are not really pedophiles, but use children as substitute object, are also removed from the game by availability of real-life adult partners.

However, what is the situation with child porn specifically ? Is it a stimulant or inhibitor of the crime ? Are there any countries, which first had availability of adult pornography only, and later lifted the ban on child pornography as well ? What were the statistics of child abuse before and after ?

All I am trying to say is, that the 2 papers from Diamond are not a proof for me, that the availability of child porn leads to lower rates of real-life child abuse. (Intuitively, I guess it is probably so, but it is not proven.)