While it is a little hard to answer a couple of the questions in there, I would recommend looking at the answer I recently gave that gets at the aims of Pol Pot.

As for regret and remorse, Sar did give an interview with Nate Thayer before he died. I will quote a relevant section

"I came to carry out the struggle, not to kill people," he rasps, his voice almost a whisper. He pauses, fixing his interviewer with an almost pleading expression. "Even now, and you can look at me, am I a savage person? My conscience is clear."

He admits that their movement 'made mistakes', but remorse and regret don't seem to figure into his views of the regime.

His beliefs stemmed from a constellation of different influences. His upbringing in semi-rural Cambodia, his move to Phnom Penh as a boy, his experience of the royal family, his education in Paris, trips to yugoslavia, the French Revolution, French Communism, Stalin, Mao and in the jungle with the Viet Minh during the First Indochina war... He had experience as a Buddhist novitiate as a boy, saw Angkor in his early twenties... he was cosmopolitan and staunchly 'Cambodian' at the same time. He is somewhat mysterious for someone trying to figure out exactly why he did what.

As for your central question, why was he such a bad guy? Well, he would probably say that he had good intentions. WE judge him as bad because of the untold amount of suffering he inflicted upon his own people in pursuit of those 'lofty goals' of the party.

Again I will quote the Thayer interview:

Trial or no trial, Pol Pot's line of defence is the same: His youthful, inexperienced movement made "mistakes" under pressure from its enemies, but they saved the country from Vietnamese annexation. Asked whether he wanted to apologize for the suffering he caused, he looks genuinely confused, has the interpreter repeat the question, and answers: "No."

"We had no other choice. Naturally we had to defend ourselves," he says. "The Vietnamese... wanted to assassinate me because they knew without me they could easily swallow up Cambodia."

. . .

Then Pol Pot, with an engaging smile, apologizes and says he needs to go back to the hut and lie down. "I feel very, very tired," he says.

He is helped to his feet, unable to rise on his own. As he's assisted down the steps and along the jungle path, he pauses to offer pleasantries to hovering cadres, who remain grim-faced. Then he raises his hands together again in a polite farewell. Before climbing back into the truck, he turns to one of his captors and says softly: "I want you to know that everything I did, I did for my country."

If you are interested in this topic I produce a podcast is trying to explain the Khmer Rouge revolution within the context of Cambodian history, for more info visit www.shadowsofutopia.com .

For the full text of the Nate Thayer interview with Pol Pot visit https://natethayer.typepad.com/blog/2011/11/pol-pot-unrepentant-an-exclusive-interview-by-nate-thayer.html