The Church is fractured into a million pieces. Christians disagree about almost everything. Even if you dislike the Catholic Church, it seems odd for any Christian to gleefully celebrate Reformation Day. You're celebrating disunity and brokenness, like throwing a divorce party.
Last I checked this is true: "For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God."Romans 2:28–29