Monsters are icons.

One definition of "icon" is that an icon is a (often graphic, image-based) symbols of concept.

A concept is a complex idea that can be expressed or communicated in a single word or image...in other words, in a single icon.

So, for example, the word "love" is a concept: the word itself denotes an incredibly complex, vast, difficult to explain set of varied ideas.

Monsters are icons of powerful emotions such as fear and moral cultural values.

Traffic Signs

The red octagon is such a common symbol of the simple concept "stop" that you can easily travel the world to countries where you don't speak a word of the language and recognize the concept "stop" immediately, just by glimpsing at the red octagon.  You don't have to think about it; the symbol says all you need to know.       

But at some point you were taught to interpret the red octagon as an icon of the concept "stop", and there really is no logical relationship between the red octagon and the concept itself: its meaning is entirely culturally constructed and must be taught and learned.  This is true of all icons.  The © icon for "love" is meaningless in most countries, cultures and languages, and, of course, the entire concept of "love" being associated with the organ that pumps our blood is itself a culturally constructed icon with no logical basis: the human emotional response "love" exists in the brain tissue, not the heart organ.
 

Some icons -- say cowboy hats or boots, or baggy hip hop pants, or tennis shoes or baseball caps -- do have a logical connection to those things that they represent, but note that their use transcends and outlives the logic of their use. Yet it is still worthwhile taking time to understand the origin of the icon. We did this with, for example, the swastika, the wolf in Little Red Riding Hood, Satan/pan and various other monster icons.

Now we understand what an icon is but we've done little to explain why they are so powerful.  An easy way to understand this power is to understand the origin of flags.

Flags

Flags are military in origin and were likely first designed to help one group recognize their own group. The predate written language, just as military conquest predates written language by tens of thousands of years or, more likely, military conquest predates the human species itself.

Either way, if you are going to wage war, the most basic necessary idea is knowing who to kill and who not to kill. The easiest way to do this is to wear some sort of clothing that delineates group -- this is as true of today's military as it was of ancient Africa as it is of gang wars in Los Angelos.

The actual development of formal flags is equally obvious: I put a symbol of my group on the end of a stick so that in the heat of battle I know where my guys are.  I put a symbol of my group on the top of my mast so that when we spot each other's boats at sea we can figure out before we meet face to face whether we should meet and whether we should meet with swords or wine casks drawn.  When I wear a helmet to keep from having my nose cut off, I need to put a symbol of who I am on my shield so that you know whether or not you want to cut my nose off.

Now step back and think of all that flags both symbolize and imply:

First, obviously, they symbolize my relationship to my group, and thus my relationship to other groups. They define who is and is not the Other.

Second, my very life depends upon my ability to immediately recognize the different flags; I cannot stop in the heat of battle and look around at the different flags and sit down and think "gosh, which way are my people and which way are my enemies?" because that will cost me my life.

Third, because my life depends upon my recognition of the different symbols/flags/icons, I am programmed to view icons with intense emotion: simply seeing the flag of my enemies will cause my blood to boil, quite literally causing my adrenal gland to prepare itself for fight or flight. Similarly, after a long battle I'm likely to weep when I view the savior symbol of my own clan.

Fourth, note how flags are inherently tied to battles for power.  As the most basic level, flags are flown over battles as a means of determining who lives and dies, and wars are fought for the right to fly one's flag over a contested piece of geography.

Fifth, because icons represent complex concepts, the flag or icon itself will mean different things to everyone who sees it: one man is willing to die for his flag to protect his right to vote, while another will die for the flag to protect his right to own slaves, while another will die for the flag to free slaves, while another simply dies for the other men under the same flag and so on and so on.

This final quality of icons -- that they are so abstract in their complexity -- actually gives them much of their immense power: because the meaning is vague and broad and subjective, it serves to unite all the contrastive subjective meanings under a single emblem.

People Kill and Die Over Icons

When we put all these elements together it becomes easier to understand why groups become so invested in their icons.

For example, it becomes clearer why every two years the House of Representatives passes legislation attempting to make it a crime to burn the American flag. Such legislation is nearly always linked to the flag's iconographic representation of the military and those who died "fighting for the flag".  On one level it seems absurd to outlaw the burning of a symbol of a legal system predicated nearly entirely on freedom of speech (and perhaps this explains why the legislation never gets past the Senate: the House vote is itself symbolic, not realistic), but on another level we begin to understand that icons are the only means we have of communicating our deepest values; the flag determines who we are willing to kill and who we are willing to die for.

It is currently against the law to publish pictures of the American-flag draped coffins of Iraq war casualties.

We begin to see why millions of Muslims took to the streets and cried for blood when a Dutch newspaper ran a cartoon depicting Mohammed wearing a bomb for a turban...and we can understand why the Muslim religion itself bans the representation of Mohammed at all: the control of the icon is the control of concept, which is, as we've said, the language of a culture's values and morality.

Now we can also see why animals like the spotted owl or wolves become such powerful icons; the battle over their iconography is a battle over "what flag flies over a given piece of geography"; in other words, we debate the icons as an effective, emotional means of debating power: the control of land.  Unlike ancient warriors or competing nation-states who would eventually settle the power struggle at the ends of their swords or guns, we are left struggling over control of the icons themselves.

Urban teens shoot each other over sneakers.