I recently attended an ICR Creation Seminar (mostly out of curiosity),
  and the reasons for the "battle" were abundantly clear.  I'll do my
  best to regurgitate them from memory.

  You can divide the world into two camps: "Christians" and "Everybody Else".
  (I know, that's overly simplistic, but let's go with it for now.)  In the
  days before Darwin, et al, life was simple:  the Bible said God created
  the universe in six days, and that was that.  Of course, this was simple
  only for "Christians" -- the "Everybody Else's" had a big problem.  So,
  the "Everybody Else's" (EE's) looked for a way to explain our origins
  without invoking God, and Darwin's work seemed to be just the thing they
  were looking for.  Now, the EE's could say:  "See, we don't need a God
  to create anything, because 'nature' can create life without God.  And
  gee, since we don't need God to create life, we can 'prove' God doesn't
  exist, or at the very least is inconsequential."  This all led to what
  "Christians" (C's) call Secular Humanism, which is basically the philosophy
  that "there ain't no God, therefore there ain't no moral absolutes,
  therefore we can do whatever we damn well please."  The argument goes
  that we all are basically just animals, and since 'wild' animals have no
  "conscience" or "moral absolutes", then we don't either, other than what
  we place on ourselves by choice.  We don't have to answer to God.

  Needless to say, this doesn't set well with C's at all.  The EE's were
  (and are) using Evolution as a tool to "prove" God wasn't necessary.
  Therefore, C's attack Evolution, because if it could somehow be debunked,
  then the EE's would lose their primary argument for a God-less universe.

  Needless to say, there's alot more detail to the story, but that's the
  "taproot" as I understand it.  If you get a chance, attend an ICR seminar.
  At the very least, you'll come away understanding *why* Creationists are
  so bull-headed in their beliefs.

  So, what's the solution?  Simple:  If *every* atheist/agnostic on the
  planet were to STOP invoking Evolution as "evidence against God", there
  would be no controversy.  In fact, I believe that if all forms of religion,
  and I include atheism here, could be exorcized from the Evolution-Creation
  "debate", then the Bible and Evolution could co-exist and even compliment
  each other very nicely.  But that ain't never going to happen, so the battle
  will rage until the end of time.

  Corrections to the above welcomed; flames will be cheerfully ignored.