The problem they are highlighting is child abuse. Child abuse is indeed a horrible thing. It's also a very hard thing to combat because it largely happens when a trusted adult abuses a child and mostly doesn't document it for posterity or share it on the internet. The victims face the double whammy of shame and social pressure not to accuse the victimizer.

Attacking the perverts sharing pictures is worthy but does almost nothing to prevent child abuse. The best case scenario is you expose a small portion of perverts and thus prevent idiots from trusting their kids with them.

Unfortunately attacking messaging services will do little to combat perverts sharing pictures as they can trivially switch to using slightly better technology.

The effect of multiplicative. Imagine you start with 1% of victimizers sharing media online. Imagine that you catch 1/10 of 1% of them before the rest figure out centralized sharing is not the best idea. You are now stuck with permanent downsides and will catch few additional people.

0.01 * 0.001 = 0.00001

The logical conclusion is that this isn't a very great way to combat child abuse.