Hi Julia,
It can indeed be "one error, you're out", and that error doesn't even have to be severe. It's merely subject to the politics, biases and whims of the elders in that congregation. I'm living proof of that.
I made the mistake of posting about this very topic in FB last week. My little sister rushed in swinging, saying many of the same things I see above. Realize those comments for what they are: groupthink with no basis in reality. Elders are held by the rank and file to be directed by holy spirit, and their actions are rarely questioned by the hive. The reality is that elders (right on up to the Governing Body!) are fallible human beings with misconceptions, myopias and hidden agendas just like the rest of us.
That realization alone is so dangerous to the organization that doubting the Governing Body as the 'faithful and discreet slave' is in itself a DFable offense.
And that, folks, is how you make a cult.