Speaking as a sociologist of religion, I think it is problematic to reify religious categories (whether Christianity, Buddhism, Judaism, Hinduism, or any other). Reification (reifying) is simply a fancy term for treating a category as a real thing.
There is no such thing as "Christianity." There are many Christianities. Indeed, members of these diverse Christianities frequently attack each other as not being "true Christians." For instance: conservative evangelicals, Roman Catholics, Jehovah's Witnesses, liberal Christians, and Mormons. Consider, in the U.S., how many evangelicals have said that they would not vote for Mitt Romney because he is a Mormon.
Religious categories are just that: categories. To understand these categories one needs to study the various, and generally very different, religious communities which fall under each of them.
As an example, I am a religious liberal. As such, I generally feel more comfortable with religious liberals in other religious categories than I do with fundamentalists and conservatives in my own category.