^ Would you enjoy Pizza if you ate it every day more than once a week? Would the comfort of the most comfortable bed be as sweet on the 86th time it's slept on than the 1st? Would Star Wars: The Empire Strikes Back be as great and fantastic after watching it nonstop for 16 years compared to once a month?
The answer to these questions is obviously NO. Without something bad to counter it, good isn't as good. Eru intended Morgoth to do what he did, and Sauron to follow, because the horror they caused and evil they spread made the love, joy, and heroic victories all the sweeter. Those beautiful moments in life are truly precious, and the eventual victories for the Holy armies mark massive triumphs that show light will outshine the dark.
Dark cannot exist without light, and without darkness, you cannot perceive light. A common theme in LotR is that a horrible evil... unites the good. Take the Last Alliance of Men and Elves, the Battle of Five Armies, the War of Wrath, and all other wars in Middle Earth. Simply look at the Fellowship of the Ring, and you will see this theme. Illuvatar knew this, which is why he made it happen.
This is true for the real world as well, which I believe is the will of God.
Namaste and may the Shadow of Morgoth never make you breed ravenous killer Orc hybrids, or rebuild Dol-Gulder.