This argument can be used to justify anything at all. For example one could use your argument to justify a preschool showing terrorist propaganda and beheadings to preschoolers, on the basis that a few of the pupils sometimes have unsupervised youtube access and therefore the whole class should learn about everything on youtube.
I’ve reached my mid-forties without knowing that something called “anal fist pumping” existed before today and I’m quite happy not knowing what the fuck that is thanks. I’m hardly sheltered, I’ve had dozens of lovers, but happily none of them were into whatever this shit is.
And not all 12 year olds have access to porn or unsupervised internet - because some of us actually parent competently. Why should families bringing their children up well, have kids coming home crying and traumatised, because their teacher showed them violent porn at school? Which has happened this year, it’s been discussed on other threads.
All teachers need immediate remedial safeguarding training to stop them facilitating perverts’ desperate attempts to groom children into kink.