It was in the MIC and security states' best interests, made popular by taking advantage of a tragedy and wielding propaganda. Honestly, GG to the people running the show at the time. It was a very clever play. Have to give credit where credit's due. We willingly surrendered so many rights.
We literally have all of history as an example of how bad Afghanistan invasions go for the invader. One prime example being the Soviet Union utterly failing just ~two decades prior.
Certainly not every intervention was a great idea, no, but that doesn't mean the right thing to do is never intervene. I'd argue the right thing to do is learn from that and not do that again.
So what interventions after WW2 do you support?
https://en.wikipedia.org/wiki/List_of_wars_involving_the_Uni...
The intervention in the Korean war?
The intervention in the Vietnam war?
Intervening in the Laotian Civil War?
The Permesta Rebellion?
Lebanon crisis? Bay of Pigs?
Invading Panama? Invading Grenada?
It provides the US military with invaluable combat experience and allows it to test/improve its strategies, equipment, and intelligence capabilities.
(Of course, fighting wars so one can remain combat-ready is the very definition of treating other people as means to an end rather than as ends in themselves, and so very much offends against the moral sensibility. But the question here is about self-interest.)
Because America recognizes the benefit in addition to bearing the cost.
Like the federal debt, we always look at only half the balance sheet to maximize sensationalism.
[edit] with this type of geopolitical posturing especially, it's very difficult to calculate the benefits of everything that didn't happen as a result of your intervention, so it's especially easy to ignore. Just like investing in unit testing. How many incidents didn't happen because of the tests you wrote - and how much did that save the company? The set is probably uncountable, but we do generally accept that it's greater than zero.
Okay but you can make the same argument in reverse that the potential uncountable benefits aren't likely to be great enough for it to be acceptable to you. And many of us have come to that conclusion.
Because we have the capacity and values to do so. In the end, doing nothing now will cost more in the long run.
If America wants to be great again, it will do so through leadership, not through self-centered isolationism. Should a gap be created, the likes of Russia and China will fill it. Is that the world leadership you want?
As I've aged I've transformed from a Ron Paul libertarian to more of a "Strong America" moderate liberal.
It's very seductive to believe that the world is a nice place and none of its issues will ever show up at our doorstep if we just leave the rest of the world alone. But sadly the world will always have strong powers and they will set the rules. I'd rather be on the winning team. If someone is going to be the world police/power-broker I want it to be us.
That's not to say we are perfect or don't need to improve. The US is deeply flawed and has caused a lot of trouble over the last century. But I'd rather be in the position we're in now vs having Russia or China be the power-broker with an even greater list of failures and abuses.
For the same reason as always - because it's in America's interest to get in the way.