Computers really aren’t very good at it, that’s another reason to worry.
For example, when Cameron decided that everyone should have pr0n filters that was that. And one of the first sites to get filtered was the blog of the MP who had been calling for pr0n filters. Because her blog had lots of works like pr0n on it.
Hugely enjoyably I was paid €7,000 for a 500 word piece which pointed this out. But however wondrous that is, my pockets aren’t really a justification for this sort of stupidity.