Even before the internet, children could get hold of pornographic magazines, or even find an adult video hidden at home. The differences with online porn are that it is currently much more easily accessible, available in vast quantities, is often more hard core and frequently extreme to the point that it would be illegal in any magazine or video available for sale in the UK. So online pornography does require a different level of protection.
Education and resilience are important too, as no technology will be 100% foolproof. A 19 year old could still show their phone to a 17 year old and only the most invasive and disruptive technical age checks could even slightly inhibit that. So we fully support media literacy efforts, for both parents and children. But equally, we didn’t previously just rely on this in the real world; society also told newsagents it was illegal to let children buy from the top shelf. Age Verification allows websites to take their share of responsibility.