Well, the filter as implemented is entirely optional - the ISPs have made it an "active choice" to enable or not - it's not something I've felt is being forced down my throat.
That it has been technically possible for a very small portion of the population to oppress their family members further does not strike me as a good reason for making it a one click option.
If you as a parent feel that this needs to be blocked, why not do it yourself on your own network? Everyone's happy then. Nation wide filtering seems heavy handed to me.