As the article says, Yee was raised as a Lutheran. I suspect that he is the product of the "liberal" form of Lutheranism, with its watered-down theology and all-too-"mainline" ways. If he had been exposed to REAL Lutheran Christianity, he would have loved Christ much too much to even THINK of converting to islam. He would also have loved Christ's people much too much to ever turn traitor against them.
This isn't just about Lutheranism--it is about all "mainline" Protestantism and much of American Catholicism, and Judaism as well. (I myself am a Lutheran.) it is the weakness, the watered-down theology, and the corruption (i.e., being "gay-friendly", refusing to stand up for Christians under persecution, etc.) of most of Western Christianity in the US that leaves the door open for many people to find a religion with more "discipline"--i..e, islam. However, what these "converts'" really needed all the time was real Christianity, for which islam is a very poor substitute indeed.
I think this represents a major failure of security (in this case the Army). The key point is not his religion, but the fact he converted to Islam and spent four years in Syria, a terrorist sponsoring state !!!. Are the officers and civilians in charge of Army clearances incompetent or reckless ? Does anyone care to speak up for the Army ?