First, the priest/penitent privilege is long-standing. Making clergy mandatory reporters would be contrary to the privilege. It is not the only privilege that would be subject to challenge under your reasoning. The attorney/client would also have to go - and with it our criminal justice system.
Second, the immunity of diplomats is a matter of international law. It often chaps but it is important. We don't want US diplomats arrested when serving in other countries on trumped-up charges. Diplomatic immunity is important for the purpose of diplomacy.
I'm less sure about the tax exemptions and deductions for churches. I suppose that would be OK if the tax exemptions and deductions for all charities were eliminated. It works for me - I don't make charitable contributions for the purpose of getting a tax deduction. However, my bet is that charitable organizations would suffer. I wouldn't want to see the government getting to choose which charities to benefit and which not.