Within specific communities it is often assumed that words like pornography, erotica, romance, and erotic romance all have fixed and universal definitions. When in fact these defintions are varied, changeable, disputed, and any shared meaning the do have is highly specific to particular communities and subcultures.
Consider for example this article about the use of sexual materials by sex offenders. Here erotica rather than being a more refined and 'worthy' subset of pornography distinguished by artistic merit, is in fact a much more broader category including things not deliberately created to be erotic at all. Specifically "Erotica can include almost any object that has become sexually meaningful to a person, including but not limited to vibrators, dolls, specific clothing (e.g., undergarments), naked orclothed pictures of a child or adult, whips, magazines..."
My point here is not to start an argument about which definitions are correct, but rather to draw attention to the fact that definitions do not generally express a pure truth about our shared reality--more often they are created by a person or group of people with a specific goal in mind. Erotica and erotic romance is often defined by authors who create or consume this work so as to distinguish it from other sexually explicit work. An approach that simultaneously elevates and demeans sexually explicit work in general by suggesting only certain 'special' forms are artistic, moral or otherwise acceptable, while others (and perhaps sex itself) remains generally shameful.
Of course when you look at the full range of sexualized material out there it is hard not to feel that some of it is in fact shameful. But I would strongly suggest that the shameful quality is not sex itself. Even the US supreme court recognizes that an interest in sex per se is healthy and not obscene. So any material we wish to argue is objectionable it must be on some other basis (the possibilities being too complex and fraught to get into here).
In other circles the goal of the definition of 'erotica' is quite different such as in the paper cited above which looks at any materials that may influence a person with a predisposition to sexual violence to develop and perhaps act on those fantasies. A categorization that explicitly does not depend on the intent of the creator of the material or its effects on a psychologically normal person. And as such leads to a very broad definition indeed.
Both of these definitions of erotica serve the purposes for which they are created. One to help people identify when sex offenders are in possession of material that may feed into dangerous fantasies, and the other to help writers described a "good" type of sexually explicit prose. But both of these definitions are built on complex assumptions about how these materials interact with the psyche of the people consuming them--assumptions that should not go unexamined.