#1 - rape as a superlative:
Many people find rape to be the highest possible pitch of evil. and in a way, I can get that - you yourself have used that idea. The idea of pain, violation, physical and mental degradation can and does color entire lives, entire communities. Get shot and sometimes you're a martyr. Get raped and you're subjected to the meta-violation of everyone weighing in on the act, what you did, what you did not do, etc. and if it's rape as, say, an act of war, then you get another layer of that shit by being the proxy for your entire race or nation that someone else wants to degrade.
Rape is often percieved as a theft of sorts - of the woman's dignity, or of her purity, or (at what I think is the worst) her family's (father's) reputation. Hence the rhetorical equation.
That being said, "rape" as a superlative is getting played out. It's phonetically arresting, and no doubt mildly titillating for some (ugh), and is suddenly ok to say because of all the hard work (many) feminists and other human rights supporters have done in dragging it out of the shadows (that last one is quite right in my book). But using it blindly like this is sophomoric and rhetorically empty. And its insulting to hear it drop out of those mouths.
#2 - rape as xenophobia/fear of the big, black (or brown) cock:
And I have another point - the connection of "rape" and its connotations with Obama and all the scary illegal immigrants. Jesus, why don't they just put "Birth of a Nation" on in the background or something?! Why don't they just sit there screaming "big throbbing non-caucasian penis!" It'd be more dignified.
Putting these ideas in conjunciton with each other is potty humor. joke about something you fear. Like a black man in power....like brown people moving into your nice little gated community...like having to look at the types of the people you ignore and acknowledge their humanity.
Instead of dealing with this, and trying to come up with sensible ways to approach illegal immigration, or mature ways to disagree with the president, they have to do this snickering Beavis-and-Butthead routine, or xenophobic alarmism (at the "violation" of such a "white" country as American...oh my stars).
Some others have opined that this is grounds for latent lust, in which case I say just admit you wanna tap that, grab a few rubbers and hit up a club or at least rent an interracial porno, calm the hell down, and then rejoin the discourse.