On technical counts, I agree. The scenario of a poorly implemented filter reminds me of "porn before the Internet": young people learning the basic tricks to gain access to forbidden material and then spreading them within their groups. Even with physical pornography, doing this was neither complex nor particularly time-consuming.

However, I maintain that there's reason for concern when a government elects to make sexuality a matter of policy. Steering public opinion in a certain direction (making the filter opt-out sounds more like a "you shouldn't be doing it, perv" rather than a "it's entirely up to you, my well-adjusted friend!") and exerting control over exposure at the infrastructure level might not be censorship proper, but I wouldn't consider it harmless from a cultural perspective. Generally, I'm indeed bothered when my government wields morality to crusade against something of dubious consequence.

Granted, this comes from someone who considers the most common stances on pornography and sexual education largely detrimental.