1) Zero is basically never the best error rate, effort isn't infinite and spending too much of it on one defect ends up meaning spending less on other issues.

2) Look at what he's saying. This is a classic pattern for providing a fake proof of evil.

a) Point to evil. For example, CSAM

b) Expand the definition of that evil in ways that are often not even evil. Here, include scantily clad in your definition of "sexual". Note that swimsuits qualify.

c) Point to examples of evil in your expanded pool.

d) Claim this points to evidence of the original definition. Note that nothing about their claims precludes their "CSAM" being nothing more than ordinary beach or pool scenes. Their claim includes the null and when the null is a possible answer it should be assumed.