This isn't a soldier issue, a religious issue or any issue. This is a man called Nidal Malik Hasan's issue. This man does not represent any group of people, because he is essentially unique. He was a single man who couldn't get married to a woman who matched his religious beliefs (you could connect him with George Sodini and all men, then?) , he was a muslim religious man who couldn't resolve it with the military's actions (therefore you could connect him with jihadists who also represent all muslims, then?) -- yet I'm not as religious as he was and still wouldn't go into the military; he made a terrible decision there which others paid for and nobody stopped. He was a deeply disturbed psychiatrist (who have -- in their profession -- elevated levels of mental troubles anyway). He had bad reviews about his psychiatric practice which weren't addressed. He wanted to leave the army and they wouldn't let him. He experienced discrimination which -- in his case -- turned out to be justified.

This situation is a confluence of multiple factors.

The Quran -- although the unquestioned authority full of evidence -- is not by itself the determinant of any one muslim's actions. It is interpreted by each individual muslim who reads it, each muslim who gains guidance from scholars, the Prophet's legacy in terms hadiths and the stories of his seera -- his life's path -- as passed on through the ages. There are schools of thought and interpretation taking it all into account responsible for Islamic jurisprudence. Muslims can reach a consensus between them. They can also be divided.

The point of meritocracy is that you decide in terms of the individual in front of you: you take into account their beliefs, their troubles and treat them based on this. You do not be blind to their ethnicity, culture or religion if it effects them neither do you assume based on religion: the most prominent example is what has happened to Christianity, there're people naming themselves Christians who only remember that when they need to write it on some Equal Opportunities form.

The first point of failure was Nidal Malik Hasan, his mistakes, his arguably self-inflicted mental hell and his horrifying indiscriminate killing. He shot at a pregnant woman. That it is justified Islamically is something only a pathological personality will believe. That he justified it Islamically when it was a grudge against the Army itself of which religion and discrimination by individuals played a part seems very likely. It was a vicious cycle: he felt persecuted and out of place due to his own choices, which resulted in him becoming more defensive and unhappy, which resulted in more isolation and a higher sense of feeling persecuted. Repeat until you have a personality feeling so victimised that you have a remorseless shooter with misdirected anger, instead of finding real solutions.

The second point of failure was the Army for retaining him in service, of which a policy of organisational non-discrimination as well as a failure of policy played a part. Why was he retained against his own feelings and beliefs, as well as giving a poor performance?

The big irony in this situation is that both discrimination and anti-discrimination played a part. This is what happens when you allow individuals to foster a victim mentality.

It doesn't matter whether a person is muslim or not. You need to listen to them and evaluate them as an individual: what do their beliefs mean to them, how are they practically applied? Is it merely lip service? What part of life's buffet is particularly to their taste? Is it family, charity, war? You must protect yourself and others from them if you see signs that are a warning.