I don’t get it. Why is any of this true? If this is true, why doesn’t the US also take in refugees from all over the world, and take over building schools or doing more humanitarian aid as well? What exactly is the moral principle that “someone” has to do these things, and why does that “someone” have to be the US?

The US does all of those things.

If no one fights off the Somali pirates, then no one can sail their shipping boats through those passages, and the US turns a net profit by fending off the Somali pirates because no one else can/will do it. That said, it still sucks that we're the ones that have to do it.

> the US turns a net profit by fending off the Somali pirates

citation needed. Given that the US military spends more than every other national military on earth combined those must be some damn profitable pirates.

I'm not saying America doesn't do any racketeering. I am saying that they get the job done though, and the job sucks.