First, as a clear-cut example where destruction is truly an act of evil we can look at the Noldor's actions towards the Teleri when they are trying to flee to Middle Earth. They ask the Teleri for their ships and, when they refuse, they kill the Teleri, steal their ships, and later burn them. After the battle we see many reactions to this wickedness despite the fact that the Valar weren't strictly allowed to stop the Noldor from leaving. After they man the ships, "the sea rose in wrath against the slayers, so that many of the ships were wrecked and those in them drowned. Of the Kinslaying at Alqualondë more is told in the lament which is named Noldolantë, the Fall of the Noldor, that Maglor made ere he was lost." There is an elemental reaction their deeds and a lament (as opposed to a poem or just a longer story) was written about the events called the 'Fall of the Noldor'. It's clear that this act of cruelty was a turning point for the Noldor after which there was no return. Mandos himself appeared to the Noldor and said,
"Tears unnumbered ye shall shed; and the Valar will fence Valinor against you, and shut you out, so that not even the echo of your lamentation shall pass over the mountains... To evil end shall all things turn that they begin well; and by treason of kin unto kin, and the fear of treason, shall this come to pass. The Disposessed shall they be for ever... Ye have spilled the blood of your kindred unrighteously and have stained the land of Aman. For blood ye shall render blood, and beyond Aman ye shall dwell in Death's shadow... And those that endure in Middle-earth and come not to Mandos shall grow weary of the world as with a great burden and shall wane, and become as shadows of regret before the younger race that cometh after. The Valar have spoken."This is quite a long quote, but it hammers home the same message over and over: by killing their fellow Elves, they have doomed themselves to a terrible fate. This passage is referred to as a 'doom,' as a 'curse', 'the Prophecy of the North', and as 'the Doom of the Noldor.' Their actions of destruction - killing other living beings that had been created by Ilúvatar - are treated with the utmost punishment.
For a second example where creation and destruction are more closely woven, we have Melkor and the Orcs. Here is a quote describing Melkor's actions:
"...all those of the Quendi who came in to the hands of Melkor, ere Utumno was broken, were put there in prison, and by slow arts of cruelty were corrupted and enslaved; and thus did Melkor breed the hideous race of the Orcs in the envy and mockery of the Elves, of whom they were afterwards the bitterest foes... This it may be was the vilest deed of Melkor, and the most hateful to Ilúvatar."This is an interesting bridge between creation and destruction that might be better described as transformation. On the one hand, Melkor is creating a new race, but this 'creation' was not done from nothing in the way that Ilúvatar performs creation. Melkor did not create the Orcs out of thin air, but did it by corrupting Elves that he found. This is also not pure destruction because he does not kill the Elves, he just renders them into something other, but that act is evil because it is a perversion of something that was good and pure.
Finally we have Ungoliant. I think that this is the most interesting example because Ungoliant creates in a very sense, but her creation does seem to be evil in and of itself. At first glance, it seems like Ungoliant merely devours (such as when she kills the Trees of Valinor) and so her evil derives from the destruction of created things in a similar way to the Noldor's Kinslaying. But Ungoliant also creates. Here is a description of Ungoliant: "She sucked up all light that she could find, and spun it forth again in dark nets of strangling gloom, until no light more could come to her abode; and she was famished." It seems that her creation of darkness is more than just a devouring / absence of light - she takes in light and actually puts forth something new in the form of 'dark nets of strangling gloom.' This may not be creating something from nothing, but the act of taking something and putting forth something more also seems like a type of creation. It is also quite clear from the description that this darkness is not neutral - dark nets of strangling gloom do not sound positive or even neutral in any way. Here is another description of Ungoliant: "Then the Unlight of Ungoliant rose up even to the roots of the Trees..." The Unlight - note the usage of a capital letter, signifying that this is something in and of itself rather than just an absence of something else - is capable of taking action on other things in the world and so it is not just a void, it is its own entity.
Very often in Tolkien we can see the bad guy as the one who runs around and destroys things. This is especially obvious when we see Sauron and Saruman destroying trees and other life. But it's not always quite so simple as that and this is clearest in the example of Ungoliant.
- V. Pressler