I never heard about spirit science until today. I don't care about it. I'll continue my studies of engineering unperturbed by people around me.
My question is... why do people who don't believe about these things care so damn much about them? Why do people want to be free to think, believe, and study whatever they want, then lash out at those who want to feel free to think, believe, and study whatever they want. I cherish my ability to study what I do, learn about the physical world how I do, and believe what I do. and I realize I have that ability because others are allowed to do the same.
If people want to believe in Xenu, let them. If people want to believe in M Theory, go ahead. A practical, sensible theory has just as much place as belief if you can't fully prove either. I remembered feeling stupid for a good long while while reading up on M-theory after believing in the Big Bang as long as I did. And yeah, the collision does allow the idea of the Big Bang, but the application of M kind of shits on what we thought the Big Bang was.
There's all kinds in this world. If you don't believe it, don't get worked up over it. Smile, take it into account what this person believes, and go about your business. You don't want people to go to forums or meetups, complain about what you believe in, and rally a cause to 'convert you to proper thinking'. So why do the same?