If religious organizations paid taxes like everyone else, NASA could send 28 rovers to Mars per year...EVERY YEAR. FOREVER.
(Total Cost of current Curiosity mission : $2.5 billion, including $1.8 billlion for spacecraft development and science investigations and additional amounts for launch and operations. )
Perhaps we should be asking questions that have to do with why we place such little importance on advancing our knowledge and more on preserving arbitrary religious orders.
Secondly, churches spend part of the money on social assistance, and so a reduction in their income may increase the funding needs for governmental assistance programs.
I'm not fundamentally opposed to cutting tax breaks for churches, but living in a country where recent tax increases have lead to a massive tax revenue reduction, I felt the need to point out that you probably couldn't fund 28 rovers with it.
As a vehicle for proselytizing. Organizations that are dedicated to social assistance have reporting requirements that churches don't. It's not transparent at all what churches spend their money on. It's a murky government-sponsored wealth redistribution scheme. Not unlike the financial industry in that regard.
...which produces more social assistance.