If I want to read about what's going on with the world, I'll read a news site. If I want to know what's going on with my friends' lives, I'll read facebook.
Your friends may not share your highly compartmentalized approach to socializing. For many people events in politics directly impact their lives; it seems to me you're asking that your friends refrain from disturbing you with information you don't want to know about.
>For many people events in politics directly impact their lives
That doesn't fit what I've seen on Facebook. A better description, "for many people, ranting about their political opinions on Facebook seems to be fulfilling for them." The only way it impacts their lives is that it was the source of their entertainment for the day.