“I believe the Pharisees did that too. Is that what you guys are going for?”
It sounds like you are more of an expert on the practices of the Pharisees than me. I will concede to your knowledge there.
In regards to Christians separating from other Christians in heresy, just read the Apostle Paul.
You are not aware, perhaps, that Christ came into the world to save sinners?
And that at every turn in His ministry He encountered the Pharisees, who were forever presuming on their own salvation and haughtily distancing themselves away from sinners?
Also: please don’t change your ground. You said ‘separate from those in sin’. Please don’t pretend that you said ‘heretics’ now.