For having red lightsabers? For wearing black robes? They're allowed to feel passion and attachement? If anything, the Jedi are evil for denying themselves those things. And Darth Plageuis for instance, he wanted to preserve life. What's so evil about that?
[Edited on 06.07.2012 8:29 PM PDT]
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The idea is that the self serving nature of the Sith is what drives them to evil acts. You need to remember that Star Wars was developed when people were less ambiguous about morals.