Among others, I recall a theory Nerys Ghemor supported - apparently, in order to reach its near-Utopian state, humanity exterminated in the past all who thought differently, all opposition.
I seem to remember Nerys Ghemor putting forward the idea that Earth may have taken dissenting voices within the greater society and "shipped them to the colonies," don't recall extermination being advocated.
According to Nerys Ghemor, those who could saved themselves by escaping in colony ships. Those left on Earth received the full treatement - violence, suppression, the works. In the end, none remained (not in hiding, not anywhere) they were exterminated.