The crusades, medieval witchhunts, and innumerable wars between Christian sects have all spilled enourmous amounts of blood in the name of this religion that professes universal love and brotherhood.
In general, modern Catholics do not believe the Bible is to be taken literally and is open to interpretation (on Oct. 12, 1996, Pope John Paul II announced that he believed the theory of evolution is correct and not in competition with religion). Protestants consist of dozens or hundreds of faiths, and it is from their number that some groups who believe every word in the Bible must be taken literaly and therefore evolution, along with most science, is wrong.
There are many different denominations of Christianity, and it is incredibly hard to estimate how many Christians there are in the United States because there is no common belief on what defines a Christian. The most liberal view of everyone who says they are a Christian being a Christian would place the figure around 75%, whereas the considerably more conservative belief that anyone outside your own denomination is not a Christian can place the figure as low as 0.1%.
Denominations sprout from the original idea of Christianity because some phrases from the bible contridict each other, and thus to harmonise this people say phrase A is literal whereas phrase B is symbolic. However, one group might say A is symbolic, but another might say B is symbolic. Thus, there are now hundreds of different denominations preaching slightly different versions of effectively the same source material.
Unfortunately, as Christianity is the 'big' religion of the Western World, it gets a lot of negative press. However, like all groups, Christianity has the best and worst among their number. The Christians who get the most press are the ones who give the stereotypical image of never doing anything wrong, and sitting on streets shout 'REPENT OR GO TO HELL', or something similarly pleasant.
However, many Christians - most, in fact - are decent people who just want the right to practice their own religion, like everyone else (or the right to NOT practice a religion, in the case of some).