Arthur C Brooks has been a registered Democrat, Republican, and now considers himself an independent.
Many people have tried to debunk his study, with little success. The study was very well done and documented, much to the chagrin of many liberals.
And for a less bombastic, more even handed definition of the American Enterprise Institute than the hysterical one you gave, here's this objective article:
American Enterprise Institute - Wikipedia, the free encyclopedia
In principle, I'm hysterical about all think tanks, which were deliberately designed to distribute propaganda and swamp mainstream media with neo-conservative and neo-liberal talking points.
But I have the same objection to liberal think tanks like the George Soros- funded Center For American Progress. I agree with some of their arguments, and since Joe Romm has joined to run their environment section, I find that of value. But, when it comes to economics, the Keynsians at CAP keep yammering about the need for a bigger stimulus package, even though making it work all depends on the economy having the capacity for continued growth. With all the oxygen sucked out of the room by Friedman followers and Keynsians, any alternative theories, especially regarding the likely scenario that energy costs, resource depletion and environmental degradation are going to make any real economic growth impossible in the future -- just doesn't have a chance to get aired anywhere but the blogosphere.
Now, getting that out of the way, I am not especially concerned with whether conservatives or liberals are the most generous; but rather the misleading and self-serving slide rule that is used to measure this generosity. I can tell you from my experiences working as a volunteer for different charities, that a charitable organization is subject to frequent auditing and has to follow a restrictive list of expense claims to maintain their tax exempt status. For a church to lose their tax exempt status they have to run it up the flagpole and advertise their gross misappropriation of church funds before the hammer falls on them. The Governments and politicians are lot more nervous about taking on a church than they are with a secular charity. A clown like Kent Hovind doesn't go to jail until he openly declares that his crazy creation museum is all tax exempt, and doesn't even make payroll deductions on employees. Even some conservative churches, such as ones in Ohio that openly declared that they were going to violate the rules of church/state separation during the 2008 election campaign have not been prosecuted or lost their tax exempt status. The liberal churches that I am aware of, tend to be old line Protestant denominations, and have little besides their church buildings to waste money on.
The study didn't ask for participants' definition of what they would call "tithing." As I stated in my earlier post, I personally consider ALL my charitable giving to be tithing, whether it goes directly to my church or not. Heck, if I give money to the Sierra Club I consider it a part of my tithe.
The church one of my brothers belongs to expects ALL of the tithe go to their church...and it has to be the 10% flat tax, or it is not following the scriptural model that was called for to support the Levites and the Temple in Jerusalem.
You're lucky if you can include the Sierra Club as part of your tithe, and limit your total giving to 10%; because my brother's church puts the call out for "love offerings" besides the tithes collected...so they would certainly tell you that you can give whatever you want to the Sierra Club; but it comes from the money you have left, and not from our cut. Needless to say, they are typical for tithing churches, that build brand new church buildings in the suburbs, equipped with auditoriums that have state of the art audio and video equipment, plus their own school, a gymnasium, fitness club with their own swimming pool....stuff you don't find at the older, mainstream denominations that still have 150 year old buildings in the downtown core!