The idea that being left wing makes you a good person is laughable, and the millions of people who died at the hands of the likes of Stalin, Mao, Pol Pot, Amin and Castro bear witness to this.
The idea that you associate dictators with being left wing is even more laughable. More people have died at the hands of Capitalism than any other political system, people convieniently ignore this, as you have by not including the likes of the social conservative friend of Thatcher, Pinochet in your list
Trotsky labelled the Stalin regime as a “totalitarian” dictatorship , a concept still relatively new in political thought at that time. Thus, Stalinism, is a form of totalitarianism, a bureaucracy, a privileged caste, at the top of which Stalin was in effect an absolute monarch who lorded it over the working class, you could make a comparison with North Korea today.
Idi Amin seized power from the left wing Obote, who was nationalising industries that meant many British companies were going to lose money so Britain backed Idi Amin's coup. It was a capitalist coup.
Castro's coup was as much a victory against US Imperialism than anything and many would argue that him going to the USSR was because Cuba had been backed into a corner by the US. Castro's coup was not a Communist coup, it included liberals, socialists and was anti imperialist. It is estimated Castro had about 15,000 people executed.
Pol Pot. I know little of apart from the KR regime did murder thousands of people. Pol Pot was a Nationalist initially who later turned to his own interpretation of Marxist/Leninism.
Mao, I find it difficult to describe China as Communist, it is more an Authoritarian state capitalist regime.
As for does being left wing make you a good person, No it doesn't, the same applies for every political ideology, it does mean though imho you are more likely to be a humanitarian.