There isn't any One Thing.
There isn't even A Few Big Things.
There's just a plethora of medium-sized things.
The list of the seven deadlies has evolved since Solomon's list:
A proud look.
A lying tongue.
Hands that shed innocent blood.
A heart that devises wicked plots.
Feet that are swift to run into mischief.
A deceitful witness that uttereth lies.
Him that soweth discord among brethren.
Proud Look being, basically, arrogance, the assumption of personal superiority. America is amazingly skilled at this one. Not at all alone, mind you, but amazingly skilled.
Lying Tongue being, not simply telling other people things you know aren't true, but also, refusing to even examine your own motives for your actions, and of course, giving your word and then going back on it.
This is not to say that one cannot change one's mind, but in a contract with others, to avoid being a liar, one must revisit the contract and renegotiate the terms, not simply drop them. The only free excuse is death.
Hands that shed innocent blood. If I have to detail this, then you're not paying attention.
A heart that devises wicked plots. A wicked plot is one which harms others to the plotter's benefit, unjustly. (Otherwise, all laws with penalties would be wicked plots.)
Let's see. Congressbeasts who hold everyone for ransom so they can make points towards being re-elected and increasing their power. Investment fund managers who create the world's largest pyramid scheme. Mortgage bankers who create bad debt out of thin air. Terrorists who scheme to murder innocents (see previous) in order to bring about their political desires. And then lie about it (I'm looking at you, Mrs. Palin.)
Feet that are swift to run into mischief. This one's probably harder to pin down, but I'll have to point out every case of presidential hubris for the last 40 years as good examples. Of course, this also happens on a local and personal scale.
A deceitful witness that uttereth lies. Not just a lying tongue, but someone who fabricates false evidence to a court of law. I could extend this without much effort to the abuse of the law to prosecute those who are revealing ugly truths. (Mr. Obama, I will not vote for you again because of your attack on government whistleblowers.)
Him that soweth discord among brethren. Now where do we see this happening? Oh, that's right: talk radio, television "news", just about any attempt to block the formation of a trade union, just about any attempt to prevent the formation of a coalition of minority groups, ...
The modern set. Using Dante's definitions where I can, as his list is the most popular commonly used:
Pride. Not the legitimate love of self, but rather "love of self perverted to hatred and contempt for one's neighbour."
Envy. The twin of schadenfreude (joy in the pain of others.) "a desire to deprive other men of theirs."
Wrath. Not anger, but anger planted, nurtured, watered and poisonous. Dante called it Vengeance, "love of justice perverted to revenge and spite."
Sloth. Acedia, the failure to utilize one's talents and gifts. But more so, this sin is the unwillingness to bother, a passive refusal to do anything beyond the minimum.
Greed. A very excessive or rapacious desire and pursuit of wealth, status, and power. Basically any sin which is based in the desire to hoard money and things.
Gluttony. The over-indulgence and over-consumption of anything to the point of waste. Usually applied to food, but it also applies to our lifestyles. Incidentally, Sloth feeds into this one as well: we waste a huge amount of resources by wanting "convenience" to a degree that we don't actually have to work to do anything.
Lust. A bit more complicated than simple sexual obsession and excess, but that's definitely part of it. Lust is failure to control (or even attempt to control) one's physical desires for pleasure. Pandering to this flaw is the basis for many of the most oppressive laws. For instance, any modesty laws enforcing crippling costumes for women so that men "won't be driven mad with desire" ... sorry, that's because the men are too lazy, proud, gluttonous, and lustful to behave appropriately.
Really, all these flaws are issues of balance. In the biblical context they're related to how they affect the relationship to God, as in, taking from God that which should be for God alone, and directing it at something physical therefore transient, or taking one's attention from God. That's a good context for those of us who believe in a God who says we exist to love one another (because we are to be like God who loves all of us).
For people that don't relate to this context, they still work. What's the effect on ourselves and on others of being trapped in these flaws?
And when you view them on a national level what do you get?