There are reasons these things frighten us I suppose. Violence and gore. That is obvious. Ghosts and spirits. Our normal defenses don't really work if they become malcontent :) Darkness. Darkness itself creates an unknown. And the unknown, within the right context, creates fear. Death. Death itself is already a fear-inducing part of human existence, and its emblems like skeletons, skulls, and graveyards invite us into the depth of that unwelcome reality.
I'm not interested in discussing the merits or demerits of horror-based entertainment. But I feel inclined to suggest that the true enemy of Halloween might be more than just an association of homeschool moms. I would suggest that the true enemy of Halloween is what some would call the transcendentals.
Transcendentals are particular abstract properties of existence. The three most commonly referenced transcendentals are: truth, goodness, and beauty, but there are others as well. Most philosophical discussion of the transcendentals relates to how these quasi meta-properties intersect with existence itself and how the different transcendentals relate to each other. It is an interesting discussion; but not one I want to have here. I would say that humans have the unique internal capacities to long for truth, goodness, and beauty. They are the foci for true human fulfillment. In academia, science, and education these qualities define the essence of what we long to discover. In film, music, and art, they are the heart of what we try to create. It is not a stretch to say that modern values that Halloween highlights are the very opposite of what is true, good, and beautiful! Let's look each of these aspects specifically.
Truth. We know that light brings to the senses what is real, what is true. The darkness conceals the truth. There is nothing more antithetical to a good haunted house than a 500-watt spot light over the whole house! Darkness (and even a little fog) obscures the reality. It makes the truth less known. The values behind Halloween can't really get off the ground when truth is relentlessly sought after or clearly put on display. Halloween thrives in the obfuscation of truth.
Goodness. Naturally, evil is the opposite of what is good. It goes without saying the only way Halloween works is if there are creatures, spirits, ghosts that have malicious intentions --that is, evil intentions. They have the potential and desire to harm you. The more depraved, the more shocking, the more cruel, the better. Goodness and virtue are the antithesis of Halloween. They not only don't go together; they work against each other at the expense of the other. There is a word for this in English... an enemy.
Beauty. Interestingly, as the end of October nears, the more hideous and the more disfigured and more fear-inducing your blow-up zombie in the front yard is, the more Halloween-esk your yard now becomes! It seems quite obvious to say that vile, ugly, and grim images (the opposite of beauty) are what make the modern celebration of Halloween work. Halloween's natural foe and greatest enemy is beauty.
Thus, Halloween's symbols and values have an enemy inside each of us. The innate human desire to pursue these transcendentals. However, occasionally our pursuit of them wears thin or our perception of them warps. At times, we don't really know what is beautiful and attractive anymore (objectively speaking). And of course, the line between vice and virtue, truth and untruth is intentionally undefined. In this void, stands a very odd holiday asking us to more creatively engage in or display (or even redefine) the entertaining value of all you can imagine as untrue, ugly, and vile. Strange indeed!