Necrophilia

You know the best thing about necrophilia? You don't have to bring flowers. Yeah, they're usually already there. Necrophilia (also called thanatophilia or getting too close to grandma) is a sexual attraction or sexual act involving corpses (dead bodies). The attraction is classified as a paraphilia by the Diagnostic and Statistical Manual (DSM; not to be confused with BDSM). Necrophilia-based tropes have also manifested themselves in literary works, film, comic books, television, et cetera.

Classification
A ten-tier classification of necrophilia as a mental disorder exists: In the DSM-5, intense sexual interest in corpses can be diagnosed under "Other Specified Paraphilic Disorder" if it causes marked distress or impairment in important areas of functioning properly as a human being.
 * 1) Role players: People aroused from pretending their live partner is dead during sexual activity.
 * 2) Romantic necrophiliacs: Bereaved people who remain attached to their dead lover's body.
 * 3) Necrophilic fantasizers: People who fantasize about necrophilia but never actually have sex with a corpse.
 * 4) Tactile necrophiliacs: People aroused by touching or stroking a corpse without engaging in intercourse.
 * 5) Fetishistic necrophiliacs: People who remove objects or body parts from a corpse for sexual purposes without engaging in intercourse.
 * 6) Necromutilomaniacs: People who derive pleasure from mutilating a corpse while masturbating without engaging in intercourse.
 * 7) Opportunistic necrophiliacs: People who usually have no interest in necrophilia but take the opportunity when it arises.
 * 8) Regular necrophiliacs: People who preferentially have intercourse with the dead.
 * 9) Homicidal necrophiliacs: People who commit murder to have sex with the dead.
 * 10) Exclusive necrophiliacs: People who have an exclusive interest in sex with the dead and cannot perform for living partners.

History
For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven. The term was coined by the  who first used the term nécrophiles in a lecture about mental illnesses in 1850 (in reference to the necrophile  who  claimed was a necrophile due to feeble-mindedness and masturbation). It derives from the Greek words νεκρός (nekros; "dead") and φιλία (philia; "love"), although there are more respectful and conventional ways to show love for the dead, such as mourning.

Singular accounts of necrophilia in history are sporadic, though written records suggest the practice was present within ancient Egypt, which would explain the obsession with mummification. Herodotus writes in The Histories that, to discourage intercourse with a corpse, ancient Egyptians left deceased beautiful women to decay for "three or four days" before giving them to the embalmers. Herodotus also alluded to suggestions that Greek tyrant Periander had defiled his wife's corpse, employing a metaphor: "Periander baked his bread in a cold oven." Acts of necrophilia are also depicted on ceramics from the – a common theme in these artifacts is the masturbation of a male skeleton by a living woman (wait, how would that work?). law from the 16th century BCE to the 13th century BCE explicitly permitted sex with the dead.

Contemporary
A modern example, was a necrophiliac serial killer. To be aroused, he had to murder his victims before performing sexual intercourse with them. British serial killer is also considered to have been a necrophiliac.

Prevalence
Time to get my shovel... Necrophilia has been observed in nature among many species of animals, including the brainy crows. This makes necrophilia perfectly fine and recommended a great argument against the appeal to nature fallacy. Biologists refer to it as Davian behavior, a name coined by biologist Robert W. Dickerman based on a limerick:"There was on old miser named Dave who kept a dead whore in a cave. He said “I’ll admit, I’m a bit of a shit” but look at the money I save.”"Another prominent animal expert is Kees Moeliker, author of the epochal paper "The first case of homosexual necrophilia in the mallard Anas platyrhynchos" and instigator of Dead Duck Day on June 5th at Natural History Museum Rotterdam.

No official statistics for necrophilia amongst the general human population exists because, as one commenter on Google Answers said: "Sadly the victims are usually very tight-lipped on reporting these crimes." Reports are skewed because cases involving murder are more likely to come to the attention of police than those involving spouses or partners who have recently passed away.

There have been notorious necrophiles throughout history, and necrophiliac fantasies are often described as more prevalent than expected. However, some necrophiles only fantasize about the act without carrying it out, as with pedophiles (although the reasons can be quite different).

Why?
Rosman and Resnick (1989) reviewed information from 34 cases of necrophilia describing the individuals' motivations for their behaviors: these individuals reported the desire to possess a non-resisting and non-rejecting partner (68%), reunions with a romantic partner (21%), sexual attraction to corpses (15%), comfort or overcoming feelings of isolation (15%), or seeking self-esteem by expressing power over a homicide victim (12%).

Wingnuttery
Some public figures of the wingnut tendency say that same-sex marriage or LGBT rights in general  will lead the world down the slippery slope to accepting bestiality and/or pedophilia,   and sometimes promoted by the evil Jews as part of their grand scheme to destroy Aryan sexual norms with Sexual Bolshevism and/or Cultural Marxism, after realizing that state Communism failed. According to Louie Gohmert, legislation to prevent hate crimes will lead to necrophilia.

This is especially ironic in the United States, as same-sex marriage has been formally banned in many states where necrophilia isn't technically illegal but will probably lead to an arrest for "desecrating a corpse" or something like that.