A recent article addressed the issue of children being frightened of costumed characters and some of the other fears they might experience.  In some cases, this fear escalated into a phobia.

However, comments like "fears likely helped our ancestors survive" generate more alarm than comfort to me. Besides being pretty obvious, it raises the question of why fear should be considered such a bad thing, especially for children.

I can certainly understand that an unreasonable fear that has escalated all of out proportion and become debilitating can be problematic. I suspect that the vast majority of fears and phobias don't actually fall into that category.
Ollendick said. "So it's oftentimes a fear that some harm or danger is going to come to them because they don't know what's behind the mask."
What could be more reasonable?  Isn't this precisely the behavior we want from our children.  Specifically I would say that it is the adults that are being unreasonable by behaving as if fears can simply be turned on or off based solely on the adult perspective of what should be considered fun or not.
"Animal phobias are top on kids' lists, with dogs being the most feared animal, followed by insects such as bees, Ollendick has found. Then come fear of the dark, stormy weather and costumed characters."
Once again, what could be more reasonable?  To a child, dogs should be feared, especially if the child hasn't been taught how to deal with them.  Insects, such as bees, can also be quite dangerous, especially if allergies may be involved.  Darkness usually makes most people apprehensive, and stormy weather may make a child fearful, depending on the violence of the storms.

All in all, I don't find anything particularly surprising about these fears, and find even less reason to think that such fears warrant treatment.  In particular, I find that too many people aren't fearful when they should be because they are ignorant of the risks involved.  How oblivious does someone have to be to fall into the Grand Canyon?  Yet it happens about once per year.  
"Ollendick treats plenty of fearful kids, ranging in age from 6 to 14 years old..."
I can understand that as children become older, one certainly expects to see fears to become more proportionate to their knowledge and experience.  Therefore if an unreasonable fear becomes dibilitating, then it would warrant treatment.  However, when one is treating six year old kids, I have to wonder what the defining criteria is.

In some cases, fears will be overcome with age, knowledge, and experience.  As they are taught how to deal with various things (i.e. dogs) they may become less fearful.  In some cases, they may well carry that fear into adulthood without any detrimental effect.

Fear is one of the most valuable evolutionary tools that animals possess, and when the behavior of adults compromises that tool it invariably leads to difficulties.  Extremely large animals are subject to being spooked or scared resulting in stampedes and running without regard for obstacles or dangers.  Many animals are "fear-biters" because they don't trust the individual or circumstances.

Are we truly so foolish to not acknowledge that our own children also have such fears as protection mechanisms?  When the people that children rely on for protection think its funny to scare them (without preparing them), then it's little wonder that they may become unreasonably fearful.  Scary movies or events can be fun for adults or older children, because they understand that its all put-on and that there is nothing to truly fear.  

An animal that has no fear is invariably a dead animal.