Nero explains it. TL;DR: think 4chan, not Stormfront:
As the leading conservative authority on interracial intercourse, I therefore feel compelled to set the record straight on the so-called racial origin and dimensions of this insult.
Here’s my verdict: all the writers above are wrong. As someone who’s been covering web culture and online memes for years and who has a great deal of respect for how well many right-wingers have taken to internet culture, I’m slightly embarrassed by my fellow conservatives’ inability to understand a term that returned to popular use not on white power websites, but on 4chan.
Before it became a 4chan meme, “cuckold” was a common term of abuse in mediaeval times and through the Renaissance. Shakespeare plays are replete with the word — that’s where I learned it, anyway, where it’s used as a byword for an emasculated male….
On 4chan, “cuck” is used as a general term of abuse, to describe
someone who caves in, surrenders, or sells out his core supporters. (His
base, in political parlance.) 4chan’s founder Christopher Poole, for
example, is called a “cuck,” not for any racially-charged reason, but
because he capitulated to outside pressure to ban controversial
discussion topics on the website. And because he was allegedly cuckolded
in real life – but not by a black man.
It’s easy to see why “cuck” makes such a good insult. It’s a byword
for needlessly relinquished manliness, for selling out and caving in.
The original metaphor of watching your partner getting slammed by
another dude now simply means abandoned principles and a lack of
backbone. It’s a byword for beta male or coward….
Indeed, the suspicion of many is that this is another case of virtue
signalling from mainstream conservatives, rather proving the point of
the hashtag and demonstrating it better than any gloss yet published. A
sort of meta-definition in action, since it demonstrates supposed
conservatives using precisely the “slander and move on” tactic so
beloved of liberals.
And I think it should be very clear that any cuckservative who would disagree with the leading conservative authority on interracial relations can only be doing so because he is a racist homophobe.
Since, you know, they don’t appear to be hypersensitive to being called names or anything like that.