If Sherlock Holmes is asexual (and I like to think he is) it wouldn't be a big deal. In the late Victorian/early Edwardian era Holmes is from it wouldn't be something people would notice. Not having sex with anyone ever except one's spouse was what society expected, so being unmarried and not wanting to get it on with someone was perfectly ordinary. These days, we're much more open about sex. We talk about it, we're generally OK with it happening before a marriage, and when it happens outside of a marriage the concern is that the spouse is being betrayed, not that the act is itself morally wrong. So these days, being asexual is something that gets noticed and is considered strange. It's not that asexuality started existing as a thing only when social mores about sex changed, it's just that it's much more obvious now than it used to be.
On a related note, another thing people seem to miss entirely when they're reading Victorian or Regency fiction, is that when characters from those eras speak of marriage, they are necessarily also speaking of a sexual relationship with the opposite sex. A male character who is not a libertine or rake or otherwise Lord Byron saying in such a novel that he is perfectly happy with never marrying means, along with not wanting the responsibility or commitment that comes with marriage, that he's come to terms with the idea of not having sex with women. Maybe its something he's willing to give up in order to retain his carefree lyfestyle, or maybe he's willing to give it up because he doesn't feel responsible enough to provide for a family (and avoiding that type of guilt is kind of really important), or maybe he's just ace.
+1
These days, we're much more open about sex. We talk about it, we're generally OK with it happening before a marriage, and when it happens outside of a marriage the concern is that the spouse is being betrayed, not that the act is itself morally wrong. So these days, being asexual is something that gets noticed and is considered strange.
It's not that asexuality started existing as a thing only when social mores about sex changed, it's just that it's much more obvious now than it used to be.
On a related note, another thing people seem to miss entirely when they're reading Victorian or Regency fiction, is that when characters from those eras speak of marriage, they are necessarily also speaking of a sexual relationship with the opposite sex. A male character who is not a libertine or rake or otherwise Lord Byron saying in such a novel that he is perfectly happy with never marrying means, along with not wanting the responsibility or commitment that comes with marriage, that he's come to terms with the idea of not having sex with women. Maybe its something he's willing to give up in order to retain his carefree lyfestyle, or maybe he's willing to give it up because he doesn't feel responsible enough to provide for a family (and avoiding that type of guilt is kind of really important), or maybe he's just ace.