Could pleasure and pain share a common source?
They are, but the noble prince or knight is just one side of the fantasy, the superficial one. The other side is deeper, darker and quite older. Blood, violence, pain and pleasure have all danced together since the dawn of time. It is a jungean archetype, rooted in our DNA, one which Hollywood and publishers do their best to milk as efficiently as possible. Vampires are just for show of course, creatures that inspire awe and terror, but also wonder and excitement.
The real attractor is blood. Along with the pain that occurs when that blood is poured. That pain induces a “latent pleasure” to some people. The reasons vary, but quite often it is guilt, the feeling (either imaginary or not) that you have done something bad and need to be punished for it - quite likely a childhood remnant. When someone feels guilt and thinks he can blunt it through pain, he may either find a "master" or a "mistress" to "punish" him or inflict pain on himself, usually by cutting or piercing his skin. Guilt is very arduous. Guilt is the ultimate, most toxic emotional poison. It is the strangler of the soul.
Some psychologists argue that it is actually healthy to express ourselves through "BDSM" (bondage, discipline and sadomasochism) and similar practices. Others do not think it is unhealthy. BDSM was until recently officially considered a "paraphilia" by psychiatrists, id est a sexual or mental disorder. This started to change in 1994, when American Psyciatric Association's DSM-IV asserted that "The fantasies, sexual urges, or behaviors must cause clinically significant distress or impairment in social, occupational or other important areas of functioning in order for sexual sadism or masochism to be considered a disorder".
Marquis de Sade was a French aristocrat, philosopher, politician and writer. He lived in the period before and right after the French Revolution, and spent in total 32 years in prison, almost half of his entire life. Before the revolution his writings were regarded as "blasphemous".
After the revolution Napoleon himself ordered his imprisonment (without trial) for 13 more years, due to "Justine" and "Juliette", two of his novels that Napoleon called "abominations". De Sade wrote extensively on sadomasoschism; sadism itself was named after him. He is the pioneer of the genre but he paid it with his freedom. The fact that he was an alleged frequent sexual offender and an aristocrat during the French Revolution naturally did not help him.
Pleasure and pain appear to contrast each other, yet they are often closely linked. Apart from vampirism and BDSM there is also depression, or at least moderate sadness. Occasionally we choose to sink ourselves in it despite the fact that happiness might just be a "go out with my friends and have some coffee" away. Why? Because seclusion is easier, more convenient, allows us to have our piece and quiet, be free from noise pollution and possible annoying friends. Or just enjoy our laziness, even when we are reluctant to admit it. So we might not really be happy but there is a "latent pleasure" in it. Should we enjoy it? I would say yes but not overdo it. We are both social and lonesome beings. The key to happiness is to find a balance between the two.