It's easy to see why, given the abysmal ignorance which characterises creationism, because it superficially seems to challenge some of the basic principles of Darwinian evolution because it appears to open up the possibility that changes acquired after conception can be passed on. This is, of course Lamarckian, not Darwinian inheritance.
Given the creationist assumption that if they can show any science to be ever so slightly wrong in any way, the entire body of science if proven false and their primitive, evidence-free superstition wins by default, they grasp desperately at epigenetics like a drowning man grasps at straws and wave it in triumph.
No need to prove the absurd assumptions and frankly idiotic, uninspired guesses on which creationism is based. Job jobbed! Praise the Lord!
There is of course one small snag.
Not withstanding that some characteristic may show signs of post-conceptual, epigenetic origin, these are very few in number and in no way affect the evidence that the vast majority of differences between species can be attributed to change in allele frequency due to natural selection, genetic drift, etc, in perfectly well understood neo-Darwinian evolution. To suggest that the presence of a few epigenetically attributable changes somehow nullify evolutionary mechanisms is of course absurd, and it still holds true that these changes will only succeed if they are at least neutral and preferably beneficial.
But a few moments thought, with a little understanding of what epigenetics is really all about, will show that it is actually a devastating rebuttal of the idea of intelligent design. Firstly, a brief explanation of epigenetics and why it evolved early on in the evolutionary history of multi-cellular life.
Multicellular organisms, especially those with specialised cells which have developed from a single cell zygote, such as just about every multicellular organism as opposed to a disorganised colony of single-celled organisms, have a problem to overcome. All their cells have exactly (with a few exceptions) the same DNA derived from division of the original DNA. However, cell specialisation requires that not all genes are active in all cells. It would be disastrous if neurons started producing the same digestive enzymes as the pancreas, or skeletal muscle began to ovulate or function as a liver. Specialisation in complex organisms requires discipline. In fact, when this goes wrong we often get cancers.
So, early on in the evolution of multicellularity some mechanism had to arise which allowed all the unwanted genes to be switch off while keeping all the wanted one active, and this is what epigenetics provides. One epigenetic mechanism is the addition of a small methyl group to the cytosine in DNA but only where a cytosine is next to a guanine. This small addition prevents the DNA being transcribed by the enzyme transcriptase to make the messenger RNA (mRNA) which then goes off to bind to a ribosome and be translated into the correct sequence of amino acids in the resulting protein. It is a bit more complicated than that, involving four proteins known as histones being attached to the DNA, but that is the bare bones of it. For more information, watch the YouTube videos or visit the Epigenetics page on the Utah University 'Learn Genetics' site.
This methylation is maintained if and when the cell reproduces so ensuring that liver cells always produce liver cells, skin cells always produce skin cells, etc.
But, to be passed on to the next generation, epigenetic change would need to occur in the specialised germ cells which produce either male gametes (sperm, pollen, etc) or the female gamete (ovum). It matters not to these germ cells what changes may have occurred elsewhere in muscles or liver, etc. because the only information that passes to the next generation comes from these cells. It is wholly contained within the gametes, either in their nucleus, their cytoplasm or their mitochondria, so this is the only information which ends up in the zygote. The zygote itself has the ability to reset the epigenetics to a condition known as pluripotency, in other words to produce a stem cell capable of founding all the cell lines needed by the developing embryo.
Now, this probably all seems very exciting for a creationist because it opens up a nice lot of gaps in the current science in which they can sit their creator god, at least until science closes it, in the hope that this time, unlike every other time science has examined a gap in detail and closed it, we will find their god still there and science, unlike every other time, will fail and they will have won. That glorious day when people abandon science and revert to magic as the best explanation for everything - like before we invented the wheel and though Earth was flat!
Why would an intelligent designer create such a complicated mechanism, which looks for all the world like multicellular organisms evolved from single-celled ones, and pack every cell with a full compliments of genes when none of them require all the genes to be functional and some require only a relative handful? Where is the intelligence in that? It's not as though most higher animals can regenerate limbs or organs from reset pluripotent stem cells because the process of methylation is normally a one-way process with specialised cells becoming ever-more fixed as they become more specialised - hence the current interest in stem-cell research.
Any intelligent designer worthy of the adjective would either make the process reversible so limbs and organs can be regrown, or would give each specialised cell just the genes it needs without the wasted overhead of reproducing all the genes plus all the methylation to switch lots of them off. It is simply not a mark of intelligence or the ability to plan to create a mechanism which automatically and obsessively replicates useless redundancy.
There is still a great deal to be discovered in this field of science but the gaps are not going to destroy science, especially evolutionary biology. Gaps are of course to be expected because the science is relatively new. Like any other new field of science, these gaps will eventually all be closed and none of them will be found to contain a god or to require magic. As Charles Darwin himself but it, "...it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science".
Epigenetics is not the saviour of creationism; it utterly refutes it. It is the product of a mindless, utilitarian process which reflects the unplanned evolution of multicellularity and cell specialisation.