[Gorwingel]

Well in one way all these "monsters" are related because in the books Tolkien does not give a very good discription of any of them. We kind of are left to imagine them for ourselves (this is a connection in response to the method of writing Tolkien used in the books).

In my opinion Shelob wasn't really evil. She was just doing what needed to do to survive, and it seemed like the Balrog was just protecting his territory.

The Black Riders, and Gollum were both corrupted by the ring (or rings). So in my opinion they kind of end up evil by accident. Gollum does what he does because he wants the ring. The Black Riders do what they do because they were attracted by the rings that were given to them, and so thus they were brought under the dominion of Sauron, and are thus controlled by them, making them evil.

I will come back to this later