Also, if you are a philosopher, you should realize that good and
evil define each other. Good is the lack of evil and evil is the lack of good. It's a casuality paradox. Without
Melkor, there would be no reason for us to revere
Manwe.
Well, I am something of a philosopher (aren't we all?), and I don't agree. See, this reasoning does not take existence into account. If evil and good are equal in stature (ontologically), then why would anything BE? Or as another philosopher put it, the great question is "why there is something as opposed to nothing?" If you agree that good and evil are equal, you can't answer this.
However, if you agree that good is the will of the Creator (that is, the will of the Creator
defines Good itself), then you see that Good has prior existence and is higher, ontologically, than evil. (sorry about the big words).
On the subject of the thread:
Eru created everything, including the
Ainur, out of love. This is why things and
spirits exist: Eru loves them. All explanations about the Universe being a plaything for
God's amusement assume that God needs amusement, and therefore is not self-sufficient, therefore, not perfect.
(I know I conflated Eru and the Christian God here... sorry about it, but like ithrynluin has said, I think they are the same and that
Tolkien intended them to be the same. A debatable proposition for sure).
So. Eru loves Melkor at the beginning -- otherwise why would he create him? A pivotal point in this question is that God does not creates things that don't have value in themselves, in other words, he does not create evil things. Things become evil, but are not created evil. The same happens with Melkor, who was not created evil (several quotes attest to that -- but I can't give them now, I'm without the
books, sorry).
On the other hand, Eru/God
is justice. Note, I am not saying that he loves justice, he IS justice. And therefore he cannot avoid being against an unjust deed, or an evil deed. It would be as if he denied that he is God.
My answer to the question is this, then: Eru can never be "upset", as I understand the word, meaning annoyed at something that is going contrary to his will. But Melkor most assuredly is going contrary to his will. So justice demands that Melkor be punished. Eru is all-knowing, and knows that Melkor will be punished for his evil deeds. But this does not "upset" him, insamuch as it is a consequence of what he is: justice.
(By the way, Eru still loves Melkor, meaning he still wishes that Melkor would repent and help with the remaking of
Arda. But it won't happen... and Eru knows it.)