Cassandra and Renegade Evolution weigh in on sex, and they're spot-on. Update: distracted by teh pr0n, I missed this even better essay.
There is only one kind of good sex: consensual. There is only one kind of bad sex: non-consensual.
Consent is what you choose. Not necessarily what you want, not what you'd get in a perfect world or if you were king or queen, not even what you would have chosen if you'd known then what you know now. It's what you choose right now, given the people around you right now, given whatever state you're in right now, given who you are right now.
If you choose to have sex with someone because they're nagging you, that's your choice. If you choose to have sex with someone because you're afraid they'll leave you, that's your choice. If you choose to have sex because you voluntarily got too drunk to think through the consequences of having unprotected bodily-fluid exchanging sex with a complete stranger (or a known asshole/idiot), that's your choice. This is the first part of taking responsibility.
If you can say no, and you don't say no, you are consenting. "No" is not the default choice. "Maybe" is the default choice. This is the second part of taking responsibility.
If you, man or woman (but mostly men) even so much as raise your hand, clench your fist, or even mention any violent act, consent is impossible. Full stop. If you're so out of it that you cannot even utter the word "no", or are unable understand what you're saying yes or no to, consent is impossible. Full stop. This is the third part of taking responsibility.
That's pretty black and white. Let's move on to the gray areas.
We in the Western world live in systems that are inherently economically exploitative. This is not a strictly feminist issue, nor a strictly racial issue, although it is definitely true that women and racial minorities are disproportionately getting the shitty end of the economic stick. Regardless, we all have to live in the real world, and we all have to choose not whether but how much we're willing to be exploited to live.
I'm not trying to defend economic exploitation. I'm saying only that exploitation is not a matter of individual consent per se, it's a much bigger political issue. Attacking the individuals who consent to a greater degree (or merely to a different mode) of exploitation is stupid, ineffective, and nauseatingly sanctimonious. Even the most degraded slave has chosen slavery over death. By attacking his or her choice, you're saying nothing but you'd rather he or she die. The effective way to fight exploitation is always to offer more choices.
Consent in the presence of an actual threat of violence--however mild--is impossible. But consent is not so easy to decide in the presence of generalized or non-specific fear, absent an actual threat. If you have sex (or do anything at all) because you're afraid of anyone (mostly men), then you have a serious psychological issue that requires treatment. It is not men's fault, nor the fault of any man. We (as a society) ought to be willing to help, but you have to take responsibility for these sorts of psychological issues, because no one else can. This is the fourth part of responsibility.
This is not rocket science, it's basic common sense.
This is America in the twenty fucking first century, not Pakistan, not 1970. The structural, institutional barriers that denied women and minorities access to the courts, to the government and to the economy have been broken. This does not mean that full equality has been handed to anyone, women, blacks, gays, atheists, pagans, or furries. But anyone can now fight for his or her personal, political and economic rights. So fight, dammit. This is the fifth part of responsibility.