A lot of this can be said for most, if not all, of the stolen-Paganism claims, not Halloween. If you excuse the inherent bias, Fr. Casey Cole has a good recent video on the matter, however, he focuses more on Christmas than Halloween: https://www.youtube.com/watch?v=DpYNQgb_IAE

Ironically, most of the anti-Christian and Pagan symbols you see today were actually copied from Christianity. The upside down cross was originally the Cross of St. Peter (St. Peter asked to be crucified upside down because he thought himself unworthy to die as Christ did), until anti-Christians used it in intentionally sacrilegious mock-rituals (https://en.wikipedia.org/wiki/Black_Mass).