The Lesson of Melkor

So in Tolkien's work, Melkor starts off as an agitating asshole. He causes problems and tries to screw up the Song of Creation. He's forgiven for it and allowed to continue on. No consequences to his actions.

When they land in Arda, he is still an asshole. He perverts creations. He smashes the Lamps. He starts kidnapping newly awakened elves and turning them into orcs. 

A small punishment is doled out. Just a small one. He promises he's learned his lesson. He promises he won't cause any more problems. He says he's sorry and things will be better.

And then......he starts sewing seeds of doubt in the elves and kills the two Trees. And commits the first elven murder. And basically, all of his lies fester into the elves going back to Middle Earth and starting a war on their way there.

Melkor is full of lies and jealousy and a need to be the Most Powerful and a need to be the Special One. A few people speak out against him, but they get drowned out by the people who just can't accept that he is as bad as he is. They keep building things back up and he keeps destroying them. 

The lesson here? I think you can figure that out for yourselves. I think you can also see how it applies to current situations.