This is coming from the same people who say "think for yourself dude" then suddenly feel the need to warp the minds of the youth into their line of thinking as a cope. When you can't wait for your opposition's children to grow up fast enough to embrace rationalism, your last ditch attempt is to do the exact thing they accuse their opponents of. What you are seeing is a negation of liberal enlightenment ideas, as soon as you advocate true open ideas, things such as tribalism, collectivisation, and spirituality win out.
I am pretty sure that the "Satanic Temple" are aware of this, they are atheists LARPing as a religion in a form of edgy irony. Simply not believing in god is not enough, living and let live for others is not enough, agreeing to disagree is not enough. You would assume that by following through in Nihilism that the logical conclusion is each to their own, nothing matters. Of course, that then leaves a void you see, there is something fundamentally empty about their worldview because it is essentially empty.
When they are together congregating and acting as one to destroy and dismantle the Christian faith, their antithesis becomes their sole meaning on this earth. Its a very hollow inversion on display for others to see, a conduit of belief for the faithless. Why bring children to these after school clubs? They know that if they do not reach the youth first, Christians eventually will, and they will not share in their beliefs about being supposedly 'open and free thinking'. Arguments and debate do not mean shit when you are faced with a collective cohesive group aspiring to higher ideals. The simple thought that parents choose to raise their kids within the Christian faith is such an affront that they must step in and do it for them.
Humans are not these rational creatures that are 'free thinking', everyone has a subconscious in-group presence and bias in everything they do. Societies and ideas are not formed on the basis of individuals but instead huge collectives. Religion provides structure and meaning to people even if that faith can be questioned, it is indeed a powerful thing. Believing in nothing does not have the same appeal or attraction, thus these 'rational individuals' form their own religion to combat it without realising the flaw in their own worldview. Now they find themselves at the point of having to ironically brainwash the youth because "OH NO, those scary Christians are going to raise their kids with principles that doesn't revolve around themselves!".