I'm starting this as a new thread, although the issue has come up in a number of different threads where some discussion has summed to:

(my paraphrase of the logic)

(1) arms are coming from the US and ending up in the hands of foreign nationals;

(2) the US has adopted the doctrine that it can intervene in foreign nations whose residents allegedly supply arms to our enemies; and

(3) the nations who are harmed by US armed sales should have the same right to intervene in the US, since the US does not take steps to halt those arms shipments.
So, there, we shouldn't intervene in foreign nations.

The factual fallacy in that argument (leaving aside the mixing of apples and oranges problem) is that the US has taken and does take steps to halt arms traffic from or through the US. Here is the latest case result.

Syrian-born arms dealer gets 30 years in prison
By LARRY NEUMEISTER, Associated Press Writer
Tuesday, February 24, 2009
(02-24) 17:01 PST NEW YORK, (AP) --

A Syrian-born arms dealer was sentenced Tuesday to 30 years in prison for conspiring to sell weapons to Colombian militants while knowing they sought to kill Americans.

Monzer al-Kassar, 63, long suspected of aiding militants in some of the world's bloodiest conflicts, was convicted in November of conspiring to sell millions of dollars of weapons to militants in a sting operation. No weapons were ever exchanged.

U.S. District Judge Jed S. Rakoff said al-Kassar and co-defendant Luis Felipe Moreno Godoy, 60, had engaged in terrorism-related crimes that were chronicled with overwhelming evidence, including videotaped conversations. He sentenced Moreno to 25 years in prison.

"I think it's fair to say Mr. al-Kassar is a man of many faces," the judge said. "It is a tragedy that a person of his intelligence has spent so much of his life in activities that certainly weren't calculated to advance the human race."

A federal jury convicted the men of conspiring to provide aid and equipment to a terrorist organization, conspiring to kill U.S. soldiers, conspiring to acquire and export anti-aircraft missiles and money laundering. The charges required a mandatory minimum sentence of at least 25 years in prison. Rakoff said sentencing guidelines called for a life sentence for both defendants, but the U.S. government had agreed when the men were extradited not to seek the maximum sentence.
Both defendants proclaimed their innocence after the judgment.