Filters simply encourage laziness...
If Child Porn is the target, or some other activity is the target, the better altho more labour intensive solution, would be to seek out and eradicate the perpetrators, or their means of creation/distribution
We all know and understand, a filter will only be viewed by those types as a speed-bump.
Try setting up email filters for ALL known spam traffic...
That alone will demonstrate the ridiculousness, its as effective as trying to prevent everyone, anywhere from uttering the F... word