What's next -- opt-in for political or religious content?
If someone desires to self-censor objectionable content -- Fine.
For any ISP (or government for that matter) to censor content without the viewer's affirmative request is idiocy.

Can you imagine the use of the opt-in lists?
Employment, insurance, licensing, etc. background checks as an example of potential abuse

If nothing else, the tin hat guys would have a field day with this.

If you think free porn is the real problem it is not.
Having customers able to spend and a product to sell that is in demand is.

In essence what you are a proponent of may end up being your own destruction.
Find a new witch to burn ...