Have you ever watched a scifi movie without the bad guys, without them there would be no Heroes, they spice up the movie, give us the creeps and make it fun to watch.
A villain (Bad guy) is an "evil" character in a story, whether a historical narrative or, especially, a work of fiction. The villain usually is the antagonist, the character who tends to have a negative effect on other characters. A female villain is sometimes called a villainess. Random House Unabridged Dictionary defines villain as "a cruelly malicious person who is involved in or devoted to wickedness or crime; scoundrel; or a character in a play, novel, or the like, who constitutes an important evil agency in the plot.