You seem to be under the impression that it is impossible to remain religious with ‘goyishe’ influences but there are hundreds of thousands of jews who are proving you wrong. Being dati is accepting the 13 ani ma’amims; accepting the torah and the talmud.
It is not being extra chumradik on various specific halachot that the haredim decided are most important. Each religious jew keeps to his own level, whether that includes watching movies, going to bars, not getting up for an old man on a bus or stealing.
Your son may be deliberating due to his lifestyle not making sense or he may may be just using this as an excuse because he wants to go out and have fun. Either way, i think the best next step would be for YOU to accept that the haredi way does not have a monopoly over 100% religious judaism and then you can try telling him that he can have his ‘fun’ and he can live as a religous jew as part of the 21st century. Then, later, if he is genuinely on the level, he may put aside films and the like for holier activities.