The odds of insemination are lower, because things like self-lubrication and uterine peristalsis (which make a big difference) aren't typically going to occur.
A quick Bing search found this:
A SINGLE act of rape may be more than twice as likely to make a woman pregnant as a single act of consensual sex.
[...]
The Gottschalls focused on 405 women who had suffered a single incidence of penile-vaginal rape at some point between the ages of 12 and 45. Of these, 6.4 per cent became pregnant. But that figure jumped to nearly 8 per cent when the researchers allowed for the women who'd been using birth control-US government statistics show that 1 in 5 of the women in the sample were likely to have been using the pill or an IUD.
To complete the comparison, the Gottschalls needed to know how many women in that age group get pregnant from one-night stands and other one-off acts of consensual sex. The answer-reported this year in a separate study by Allen Wilcox, head of the epidemiology branch of the National Institute of Environmental Health Sciences-was a mere 3.1 per cent. "It was surprising to see this margin of difference," says Jon Gottschall.
Did they account for people having consensual one-night stands possibly using condoms more often than rapists ?
One of the lessons highlighted in the thread "Less Wrong NYC: Case Study of a Successful Rationalist Chapter" is Gender ratio matters.
There have recently been a number of articles addressing one social skills issue that might be affecting this, from the perspective of a geeky/sciencefiction community with similar attributes to LessWrong, and I want to link to these, not just so the people potentially causing problems get to read them, but also so everyone else knows the resource is there and has a name for the problem, which may facilitate wider discussion and make it easier for others to know when to point towards the resources those who would benefit by them.
However before I do, in the light of RedRobot's comment in the "Of Gender and Rationality" thread, I'd like to echo a sentiment from one of the articles, that people exhibiting this behaviour may be of any gender and may victimise upon any gender. And so, while it may be correlated with a particular gender, it is the behaviour that should be focused upon, and turning this thread into bashing of one gender (or defensiveness against perceived bashing) would be unhelpful.
Ok, disclaimers out of the way, here are the links:
Some of those raise deeper issues about rape culture and audience as enabler, but the TLDR summary is:
EDITED TO ADD:
Despite the way some of the links are framed as being addressed to creepers, this post is aimed at least as much at the community as a whole, intended to trigger a discussion on how the community should best go about handling such a problem once identified, with the TLDR being "set of restraints to place on someone who is burning the commons", rather that a complete description that guarantees that anyone who doesn't meet it isn't creepy. (Thank you to jsteinhardt for clearly verbalising the misinterpretation - for discussion see his reply to this post)