When organized religion is kept out of public schools, with time, religion slowly fades away as there is less need for it.

Is there data to support this? As much as I would love that to be true, I've got my doubts. Most religions are not taught in western schools. Despite that, parallel societies are established where a specific religion is fostered. Children are sent to private religious schools and the religion is uphold by these communities.

(This is not an argument against secularism. I'm indeed in favour of keeping proselytizing subjects out of school. Just questions the effect on the evolution of religious demographics.)