Anakin - "If you’re not with me, then you’re my enemy!"
Obi-Wan - "Only a Sith deals in absolutes!"
Both Anakin and Obi-Wan wanted the end of conflict. Both wanted the return of order to the galaxy. Only the means differed, not the ends.
It is temptingly easier to give in to the dark side -- fear, anger, rage, desire for power -- and tapping into those emotions may even be a shortcut to power... but the abuse of power inevitably leads to tyranny, injustice, and suffering. It always has, and it always will.