And you think courts should be arbitrating every time some internet message board bans someone for posting porn or spam or a swastika? Because that's the implication of what you're saying here: let's let courts handle it.

Is this a serious suggestion? The courts are already overwhelmed, packed full of cases. And you want to throw potentially millions of minor cases where someone's mad about getting banned for flaming some other user onto their docket?

Politicians aren't a protected class under US discrimination laws. A politician banned from Facebook would generally have no legal grounds to sue.