Well that's because right wingers gleefully extoll the mass murders by left authoritarian dictators, while completely ignoring the millions of people murdered by right wing authoritarian dictators, or the various and assorted genocides by right wing authoritarians over the same time frame.
Perhaps it's because the USA either installed or propped up many of those right wing authoritarians over the past 100 years. Because right wing media only tells them bad shit about the left and never the right? Who knows? I really don't understand why right wing American do ANY of the stupid shit they do, other than out of desperation to defame the left, and to retain power.
Authoritarian dictatorships on either side of the political spectrum always resort to murdering their own citizens to suppress and terrorize the opposition. In South American, right wing dictators tortured and murdered all of the left wing lawyers, labour leaders, and university professors. In Argentina, they're called "The Disappeared".
Move is part of groundbreaking effort to name 30,000 murdered by regime after 1976 coup
www.theguardian.com
Before the Gulf War, the USA was giving weapons and support to Saddam Hussein in Iraq. Another mass murdered.
In Chile, they lined leftist leaders up in the soccer arena and murdered them:
Political prisoners were routinely executed at a soccer stadium in the Chilean capital, Santiago, after the 1973 military coup, a former non-commissioned officer has claimed.
www.theguardian.com
The reason Iranian say "Death to America" is the Shah of Iran, who the USA kept on the Peacock Throne for decades. He made Saddam Hussein look like a choir boy.
And of course Adolf Hilter who is responsible for more than 50,000 deaths in WWII and the camps.
And of course there is the genocide of indigenous peoples throughout North and South America over the past 300 years. Americans rarely acknowledge that.