The answer to this question is obvious. For two thousand years Christians have debated the relative importance of primary versus secondary causation--miracles versus laws. Evolutionary thought arises from the secondary causation camp. It is a rather extreme position, mandating that the world's origins must have occurred strictly via naturalistic causes. From Roman Catholics such as Nicolas Malebranche to Anglicans such as Thomas Burnet and John Ray to Lutherans such as Gottfried Leibniz and Christian Wolff, seventeenth and eighteenth century evolutionary thought was not merely growing, it was supremely confident. Here is a typical example of this sentiment, as expressed by Wolff, a leading Lutheran theologian between Leibniz and Kant:
The natural way, as the superior way, must always be preferred over the way of miracles, and therefore miracles cannot occur except where God cannot achieve his goal in the natural way.
And by the way, as Wolff explained, there are no such instances except in the initial creation act. Enlightenment thinking mandated evolution, one way or another. Darwinian thought was the result. It lies safely within this genre of thought, and Darwin rehearsed the many Enlightment mandates for naturalism in his arguments for the new theory of biological origins.
Today nothing has changed. Evolutionists share the metaphysical certainty of their progenitors from earlier centuries, and their proofs are based on those same Enlightenment beliefs about what god would and wouldn't do.
None of this is speculative. Anyone can read what the evolutionists have been saying. From Thomas Burnet three centuries ago to Ken Miller and Jerry Coyne today, the writings of evolutionists are available for all to see. They are certain of evolution, and their reasoning is religious. Evolutionists give plenty of proofs for their certainty, and the proofs always entail metaphysical assumptions which are imposed on the science.
But a curious thing happens when evolutionists are confronted with their own words. When you repeat back what they have been saying for centuries, and what their proofs are based on, they suddenly deny their entire thesis. None of this, according to evolutionists, is relevant. All those arguments for why evolution is a fact, they were just an aside. All those metaphysical interpretations of the evidence that contorted biology, they are meaningless.
Upon sober reflection, it seems that all the theological and philosophical arguments, used for so many centuries, actually have nothing to do with evolution. Those statements, after all, were made in haste. And those evolutionists who made them were simply lazy, or angry, or both. And weren't those statements merely retorts to those creationists in the opposing camp?
Certainly you will find no such statements being made today by serious evolutionists. Wrong. Certainly you will find no such statements being made today in serious textbooks. Wrong. Certainly such statements play no role today in evolutionary thought. Wrong.
Of course evolution's metaphysics are in opposition to the creationists. That's the whole point. Evolution's traction arises in its contrastive reasoning. The creationists are wrong, so we're right. It is not the metaphysics that are irrelevant, rather, it is the evidential problems that are irrelevant.
Evolutionists are certain of their theory, and their certainty arises from their metaphysical position. They cannot then drop the metaphysics and maintain the certainty.