Ehrlich – it’s not so bad if your son thinks that chabad is the best way to serve Hashem. The trouble is that neo chabad believes that it is the ONLY true way of serving Hashem.
But serving Hashem isn’t even what’s prioritized; it’s all about doing the Lubavitcher rebbes will, spreading his vision, and doing it FOR him, as you can see throughout this thread and others.
Chabad in the 80s was still rational. While rabbi yoel kahn was among the most reasonable of neo chabad figures, i think you should get him interested in Rav Moshe Wolfson, a prominent Mashgiach who has transitioned many litvishe boys into chasidus, and built an entire community around this – emunas yisroel. He held of the Lubavitcher rebbe, and was close with him – but he was also close with satmar; he has a balanced mahalach.
I know people who he directed towards chabad chasidus, but kept them away from the crazies. Learning in his beis medrash, which has people of all ages at all times of the day, is a good idea, i think.