So do you think campaign contributions should be tax-exempt, then? You need to get a better understanding of what constitutes censorship - there are plenty of people, for example, who wail about what they perceive to be censorship on FR. However, FR is a VOLUNTARY association, and JimRob has the right to restrict that association, and it is not censorship to limit what someone can say on FR. Now, if the government tries to limit what you can post on the internet, with only a few restrictions similar to shouting "FIRE" in a moviehose, then that would amount to censorship.
Likewise, a church can choose to become a tax-exempt organization - under the terms and limitations for such. If they find those terms too onerous, they can refuse the tax exemption. Thousands of groups make that consideration every year. McCain-Feingold is censorship because it is forced with little recourse. Limitations on political speech for tax-exempt organizations do not cross that threshhold, as there is recourse and the status is voluntary.