Genocide itself is unethical. That is what Pol Pot and his party Khmer Rouge enforced his beliefs onto the country, and executed all people who were educated "incorrectly" and stood up to him. It is unethical to commit mass murder to enforce one's political beliefs onto one's country. Therefor Pol Pot's methods of enforcing agrarian beliefs are unethical
Pol Pot unethically forced his people into a Communist farming state, which would have been bad enough on its own but then anyone who stood against him or the Khmer Rouge (Academics, dissenters, rival politicians) were executed in a way that rivals the brutality of the Holocaust. It is one of the most well documented mass killings in history.
Pol Pot used brute force, torture, murder, genocide, and general terror to force the people of Cambodia into agrarian socialism. He took people from good jobs in the city and forced them to work on the land, separating families, and working people to death. I don't see how anyone could call this behavior anything but unethical.
Some people say there is not much difference between communism and socialism. Communism is just a more intense version of socialism. Anyway, he did force his rule onto his people. Meaning, he was acting unethical to the way most societies view his actions. The people eventually were fed up and took a stand by overthrowing his government.
Ethics are for those people with the luxury of not running a country. Machiavelli pointed out that it is good to be an ethical leader, but sometimes a leader is forced to do things that are unethical in order to maintain the state. That is what Pol Pot was attempting to do when forcing agrarian socialism. He was trying to make a good decision for the country without the confines of ethics.
I do not believe Pol Pot unethically forced agrarian socialism on Cambodia. There were a lot of different forces at play that led to Pol Pot taking the lead and he didn't even remain there long once he did attain power. There's far too much going on in Cambodia at this point in history to say that Pol Pot was the only one for agrarian socialism.