According to the Telegraph, the UK government is instituting a code of conduct for public WiFi which would require blocking of pornography to protect kids.
I see a couple of problems here.
1) Porn proliferates very quickly, so the blocking is likely to always be behind the curve, and kids are really good at getting around these kinds of blocks.
2) Some people will feel that things are allowed that should be blocked.
3) Inevitably legitimate websites will be blocked. A common example is breast feeding web sties, which frequently get caught in these kinds of nets.
4) Implementing this requires active monitoring of the activity on the WiFi which generally enables other kinds of surveillance.
Most home networks don't have filtering on the whole network, so kids at home would be exposed to raw Internet. The standard is generally to filter at the end device. It seems to me that would be the best option here.
Parents could choose exactly the blocking technology and philosophy they want to have applied, and it does not impact anyone else.