The scene in question was a brilliantly dark one and the sperm in question is actually the least important aspect of it. What makes the appearance of the liquid most interesting is the fact that it wasn't played for laughs - far from it. As with the best moments on the show it actually has something to say, unlike say Californication. On one level it portrays the reality of a generation of men whose sexual education is conducted online.
So when they get with real girls, they are in effect working to the script of a porno. Adam has already shown himself to be somewhat retarded in this department, but unlike the time he engaged in another bout of selfish, uncomfortable sex, ending in relief on the chest, (with Hannah), this time he didn't ask.
What was most revealing about the scene was that this was actually his meat-headed way of breaking up with Natalia. Sure, he ordered her around on all fours (the episode was called On All Fours) but she had previously been direct with him about her rules of sexual engagement. In a sense you could say she asked for it with her "I'm on the pill but I want you to pull out and come on me just to be safe." It was confronting, uncomfortable and possibly genius.
The sight of male reproductive mucus on TV has been a rare thing, although something that is rarer in real life, female ejaculate, has been seen flying in a particularly memorable scene on Californication.
Another HBO show, Sex and the City has also been there, though I wonder if that scene, which apparently involved flying semen in a tantric sex session, remained intact on New Zealand screens when it aired here on free to air TV. (That and a scene from American Dad are mentioned in a Slate piece on Seminal Moments here.)
It all highlights the strange hypocrisies that we live with. We all happily laugh at that scene from Something About Mary, when Cameron Diaz has it stuck in her hair, but if it starts flying through the air, we call the Broadcasting Standards Authority. We are happy to watch graphic violence and mortuary carve-ups of cadavers but will not countenance female genitalia or an erect male penis. Save the whales, pass the lamb kebab; I guess that's just human nature.
This goes some way to explain that while the truly disturbing aspect of the scene (namely Adam's sexually aggressive treatment of Natalia), was seen by the Australian viewers of the Showcase channel, it was the semen that was censored out.
As TV Tonight reports, "Showcase edited very little out of the scene but shots of the fluid were excised."
It may also be that while older viewers found the scene somewhat shocking, it was not such a big deal to the kids. As the LA Times points out: "To younger viewers, who have been exposed to graphic sexual images via the internet for years, any concern over the scene might be seen as much ado about nothing. On social media, the scene was talked about -- but not as much as a scene in which Dunham's character Hannah injures her ear with a Q-tip."
