While I can't personally attest to a fear of clowns, I can see where they might disturb you.
My son seems to think the clowns in "Dumbo" constitute a separate species -- a monstrous notion quite in keeping with the writings of Thomas Ligotti. After all, the behavior of the clown is innately unpredictable, their actions often wild and exaggerated. And of course there's all that death-white grease paint to consider, the relentlessly mono-emotional painted faces and the mystery of who -- or what -- lies beneath.
But let's be honest: The fear of clowns has become something of a fad, and even more of a cliche. In fact, according to author John G. Robertson, the term "Coulrophobia" is almost certainly a product of the Internet alone and doesn't pop up in any of the expected literature. We've simply consumed too much dark clown imagery over the years in every possible medium. Fino Rohrer's 2008 BBC article does a nice job of highlighting the history of this, from Lon Chaney Sr. and the films of Jacques Tourneu to Stephen King's Pennywise and John Wayne Gacy.
Clowns in the Children's Ward
According to a 2008 study from the University of Sheffield study of more than 250 children, kids ages 4-16 strongly disliked clown imagery. Nursing Standard magazine published the study, which should give you an idea about the primary concern here: clowns at children's hospitals. By and large, the findings suggested that clowns were a relic of a bygone era and that such odd and potentially disturbing characters were best kept away from sick children.
But then again, the hospital setting is highly unsettling to a child, as I can attest to after spending a night at Atlanta's excellent Children's Hospital. Even the friendliest nurses are often met with distrust or terror, as are virtually anything unfamiliar or new. It's hard to blame the clowns too much on that count.
Clowns vs. Santa
In Rohrer's article, Clinical psychology professor Paul Salkovskis points out that children are far more susceptible to extraordinary and unusual imagery. As a result, clowns may seem scary. I'll submit that this is particularly true since the clown no longer reigns supreme in children's entertainment.
For instance, shopping mall Santa Clauses invoke just as much terror as the clown, but we give Santa a pass since we continue to champion his over-all image of nostalgic feel-goodery -- and this in spite of the many dark and horrific interpretations of Santa you'll find in horror movies and even children's TV shows. History is written by the victors, while the losers are cast into the shadows.
It may no longer be the Age of the Clown, but plenty of costumed merry-makers continue to ply their trade. I even saw a she-clown at the Atlanta Children's Hospital last week. She wasn't wearing much in the way of make-up. I believe she had a musical instrument. And she was certainly inspiring smiles.
Now, lay back and tell me about your clown phobia.