You say that there are three major presuppositions that evolution believers must make to come to the conclusions that evolution brings. You say these are:
(1) that there is an objective reality
(2) that evidence tells the truth about that objective reality
(3) that we can understand objective reality by understanding the evidence
What you fail to understand is that these presuppositions in no way hinder the value of the conclusions. These presuppositions are universal in nature, and are found in every single area of science and thinking known to man. These are conditions we believe, no, that we know to be true that allow us to make any conclusions about our world. Not only does this apply to the concept of evolution, but it applies to the concept of mathematics, medicine, computer science, forensics ( which ends up usually with the right answer, putting the right person in prison), anthropology, and even religion, namely because the writers of the Bible, the Qu'Ran, and the Bhagavad Gita were still subject to these base presuppositions in their endeavors. Are you challenging the base of modern mathematics and physics? If with these presuppositions we are able to make valid claims about our universe, such as the claim that 1+1=2 and that things fall downwards at a rate of 9.8 m/s^2, then we can show that these presuppositions are valid, and because they are, they have no adverse effect on the conclusions of any branch of science, even religion.
But perhaps the most important thing is this: Creationists and proponents of ID are also under the influence of these presuppositions. Their claims that the world is too complicated to have come up by "chance" (which is not at all what evolution says anyway) are subject to the same crime of having the presupposition that "there is an objective reality" and that evidence points to the truth and so on.
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