I understand, but the main problem and the immediate danger is not the piercing or the movies and the like. Tell me, how is he planning to pay for his new lifestyle? Which is much less frugal than yours, not to mention that he’ll need some place to live. I am really concerned he will sooner or later do something stupid, and in the secular world there is very little leeway. He does not have many people to rely upon, much less people to whom he feels he can talk freely about everything and that will support him. A small mistake that under ordinary circumstances would be nothing, people learn a lesson and go on with their life, can be the beginning of a nightmare R’L. I do not know if you should be blunt (eg what to answer when he asks if you’d kick him out) as I don’t know your son (not that I am aware of) – but I do think you should worry about serious issues, such as being arrested and possibly going to prison R’L, such as getting serious diseases (eg from “cheap” piercing or tattoo studios, Hep B is everywhere in Israel especially recently with all the immigration) R’L and believe me there are many other health issues which require a good doctor (I have the impression he does not have one he trusts with confidentiality, and anyway would be too embarrassed), and have you considered the risk of feeling overwhelmed by shame (at whatever trouble he runs into and is about to become known in public), and R’L very bad things can happen in this case too.
I also believe you should also worry seriously about your other children, I believe you are underestimating how much they are suffering and what is at stake. I realize you are very worried about your son’s observance, but you have to try to keep your head cool, especially if you keep into account that other community members may feel some steps are necessary in order to protect themselves and their own children.