almost every time someone does this - it's either focusing on determining/proving if there is a direct line between horror movies and the desensitization of the viewer (like this one obviously was)
or
why do people watch horror movies. the answers invariably being :
- the roller coaster thrills - provokes an emotional reaction that makes me feel alive.
- i like being scared
- i like to face my fears/mortality
for your desensitisation research - check V's thread :
http://www.horror.com/forum/showthread.php?t=33781
for some better information.