Earlier quoted context omitted.
The slippery slope from here to banning under 18s looking at websites discussing suicidal thoughts, transgender issues, homosexually and onto anything some group of middle age mothers decide isn't appropriate seems dangerously anti-fallacitical.
While I completely understand the slippery slope concept, we ban all kinds of things for under 18s based on morals. Why couldn't these be any different? How else does a society decide as a whole what they are for or against. Obviously, there should be limits.
These digital checks, if done "right". Are cheap to implement, and hard to get around. They don't easily let adults allow a kid to do it anyway. And a government can trivially check if a whole swath of businesses is implementating it.
That last point makes it very easy for governments to use this for widespread ideological interventions. With very little option for others to push back, because few people are involved in enforcement.