I really don't see what his emails have to do with the 1st amendment.
Locking Hasan up months ago because he sent those emails would have been absolutely unconstitutional, and I'd be the first person to stand up and say that.
Depriving someone of their rights because of what they have said is WRONG. Locking someone up for saying something unpopular is the kind of thing they do in France to those who refuse to knuckle under to the dictates of Political Correctness. It is not what is done in a free society that values the open expression and exchange of ideas, no matter how unpopular.
Being a member of the US military is not a right. Being in a position of trust is not a right. Subjecting someone to scrutiny and careful surveillance on the basis of what they have said is not a violation of their rights, but common sense.
If I say "I want to kill Bob" and the police overhear me, it would be utterly wrong for them to arrest and incarcerate me on the basis of that statement alone. However it would not be wrong for them to keep a closer eye on me, and perhaps to warn Bob about what I'd said.
Diversity is a leftist nothing-word. It means nothing. America is a melting pot of people from a multitude of heritages, cultures and ethnicities. There is no special effort required to ensure that individuals from these various backgrounds live and work together as this is the inevitable outcome of their mere co-existence.
Tolerance is a good thing. Picking on someone for dressing differently, eating different foods, or practising a different religion is wrong. That being said, tolerance of difference does not and should not require the tolerance of evil. Your post-modernist liars will whine and claim that judging other cultures is wrong (and even impossible) because the notions of morality are culturally specific. This is bullshit. Right and wrong may not be ideas that are universally agreed upon, but they are universal truths. Some things are right, other things are wrong, and which is which can be known by the effects and consequences that ensue from each. In many cases one or more things may be right or wrong at the same time, with the difference being a matter of degree.
Tolerating that which you believe to be evil (not just different) is not a moral virtue, it is moral cowardice.
Many Muslims living in America speak a language other than English. This is a difference that should not be disparaged because it is not wrong in any way. Naturally they should be able to speak English as well if they expect to function in an English speaking country, but that is a pragmatic concern, not a moral one.
Many of these same Muslims are also extreme misogynists. This is a difference that should NOT be tolerated because it is demonstrably EVIL. Muslims who practice misogyny should be publicly humiliated and punished just as non-Muslims who do so are.
This is but one example, there are many others.
At the same time, there may very well be moral lessons that the greater society can learn from Muslims or their sub-cultures. The pursuit of moral improvement goes both ways. In a melting pot society, the virtues and positive values from all contributors are blended together, not melted away by the dominance of one.