Well, as I stated above, the Sith are not necessarily evil, nor are they the 'bad guys'. The Star Wars movie franchise paints the Sith as nefarious villains because of Darth Sidious, Count Dooku, and the little bitch known as Darth Vader. They are all sorry excuses of a Sith, in my opinion. Pretty much any Sith who follows the 'Rule of Two' has been worthless... It's such a stupid philosophy that was written into the Sith ideology by Darth Bane and has since severely crippled the power of the Sith Empire (again, in my opinion).
True Sith come from the Old Republic era, and you will find a small handful of those Sith who are not at all truly evil. Now, the Dark Side draws its strongest powers from anger and hatred, and I'll give you that channeling these emotions is almost always a negative thing, but the 'Dark' Side of the force is not inherently evil in and of itself. While anger and hatred draw the strongest powers from the Dark Side, Dark Side powers can also be fueled by love. Love, like hatred, is largely frowned upon (or straight up forbidden depending on who you ask) within the Jedi order for this reason. Good and evil are a matter of perspective when it comes to the Force and as I said before, I know for a fact that I would be a Sith if such things were part of our world.
I am not a bad person, but I would not be able to simply bottle up my emotions and forsake the rest of the world to a fate pre-determined as the Force decides. In that aspect, I would say that it is the Jedi, not the Sith, who are evil. There have been a number of instances when the Jedi could have stopped, or at least tried to stop, a tragedy from happening, but chose not to because it would have violated the precious code of their order. They are entirely apathetic and that makes them more dangerous than the Sith. At least you know where you stand with a Sith. You can never truly know with a Jedi, who would betray you in a heartbeat if it was in the best interests of the Jedi Order or the Force.