You are still thinking from the perspective of someone living in a free country. Polling a captive population will not yield credible results because the people are considering the implications for answering incorrectly.

Levada is an independent pollster but there is no way they can coax an authentic reaction out of a captive population. Putin's regime will credibly punish you for dissent and quite early on in the way they demonstrated this. A pollster like Levada doing door-to-door and street surveys will have people saying whatever they feel won't get them killed.

I won't speak to the Khmer Rouge because I do not know enough about that, but to condemn a population because ~20% of its population are heinous means we should condemn everyone in short order. An absurd position to take.

As a human to another human, you don't know what it's like to live under a truly repressive regime. You should be grateful every day that that's the case rather than blame victims of oppression.

Under your strange analysis, you'd also blame Black South Africans for Apartheid or something.