Yes, what everyone must remember is that a loss of tax exempt status means not only the organization pays taxes but the donors do not get a tax deduction. That is HUGE.
Many churches spend pretty much every dollar they take in. They have salaries for clergy and support staff, maintenance for the building and property, etc. Typically, money that is left over is used for missionary work whether overseas on within the community or both. Many might have a prudent reserve fund, but this will typically only carry them for a few months.
Keep in mind that it is not only taxes on income that the churches would pay, but property taxes. Many churches sit on what is extremely valuable land; it may have been cheap when the church was built decades ago, but it's prime real estate today.
If the churches are forced to pay taxes, something will have to be cut and these cuts will directly impact the members of the congregation.
Finally, there are the donations themselves. Obviously Christians are supposed to tithe graciously, but that doesn't mean that they don't take the tax deduction into account.
Basically, this would create a ripple effect that will really harm many churches. They will be faced with a huge increase in expenditures due to taxes and they will have a drop in revenue due to loss of deductions, it will cripple them.