Yes, the world has an obligation to intervene when crimes against humanity are being committed. Sometimes we do, and sometimes we don't. No one had to stomach to go into Afghanistan in the 90s, because the Soviet debacle was fresh in the popular consciousness. "There's a lot of fucked up shit in the world" isn't a valid argument for ignoring regimes that are as egregious as the Taliban are. The fact the we think negotiating with them is a viable "peace" strategy now means that the whole war has been fought in vain. Shame, really.
Do we though? Let's assume that the point of interventions in other countries is the common good, just to give things the benefit of the doubt for a brief moment (its clearly money and power, always has been and always will be.) By invading Afghanistan, what has been accomplished? Well, the Taliban was temporarily removed from power. The United States became further involved in the Middle East, usually to the detriment of both regions. Civilians have died in the thousands. Democracy has proven to be ineffectual was imposed by an external force. That's not taking in to consideration the massive economic damages of the war in Afghanistan and the almost inseparable war in Iraq. Trillions of dollars spent, and down the road several trillion dollars of benefits for veterans that people around my age are going to have to pay. The economy has suffered vastly, and the cost of the war on the United States has made mincemeat out of what was once a very balanced, logical budget. Life is a series of horrors. Right now in Mexico there is a woman having her breasts flayed by drug cartels. Children starve by the millions, people die in the streets, religious centers are bombed, human potential goes to waste. In India, the undesirable castes shovel shit in sewers for no pay. North Korea is still actively running concentration camps. Right now, in an airport somwhere in the United States, there is a woman being molested by a TSA officer, and she will say absolutely nothing about it because she's afraid what will happen. None of those issues, or the thousands if not millions of others out there are going to be solved by the United States. They can't be. Yes, it is depressing that the world is full of people ready and willing to kill over disagreements or ruin people's lives for the sake of ideology, but is that worth the death that war brings? There's anywhere between 100,000 to 1,000,000 dead Iraqis from that war alone, depending on what study you go for. Afghanistan doesn't even have solid numbers as best I can find; its somewhere in the tens of thousands. Yes, there are times when the regimes are horrible, and there are times when you look at a country and hear what people are saying and you want to help. But a good government knows that its rarely worth it, because the end result is just more death and a return to the status quo. The only difference with these deaths is that they're not "crimes." They're just collateral damage.