​In its 1970 opinion in Walz vs. Tax Commission of the City of New York, the high court stated that a tax exemption for churches "creates only a minimal and remote involvement between church and state and far less than taxation of churches. [An exemption] restricts the fiscal relationship between church and state, and tends to complement and reinforce the desired separation insulating each from the other." The Supreme Court also said that "the power to tax involves the power to destroy." Taxing churches breaks down the healthy separation of church and state and leads to the destruction of the free exercise of religion.

http://www.latimes.com/la-oew-lynn-stanley23-2008sep23-story.html