If Darth Sidious appeared at your doorstep would you answer the door?

The opening of Episode III says, "...there is evil everywhere".

People have raised the issue as to how one can know if something or someone is "good" or "evil" or if such concepts even exist in the real world. Star Wars did a good job at appealing to our gut instinct in that it's clear that characters like Darth Sidious are the "evil" ones and the Jedi, like Obi Wan, Mace Windu, or Yoda are the "good" guys.

So what is it about these characters that enable us to instantly know they are good or bad? One of the posts under my previous topic said that good and evil are subjective and don't actually exist, yet one would be hard pressed to argue for Darth Sidious being the good guy, especially after his order to kill the adult and child Jedi's.

So how is it that Star Wars has no problem conveying who is evil and who is good? The movies don't go into any deep religious or philosophical meanings to define good or evil, yet the viewer can quickly and easily identify who is evil.

What is it about the characters that enable us to know they are good or evil?

Do you think the concepts of good and evil can be universally known or are merely relative?

What standard do you use to determine if something is good or evil?