But yes, admittedly, the United States has supported autocratic regimes due to strategic concerns elsewhere. In many of those cases, it was a calculated tradeoff between allying with a single military regime such as Turkey—which would not have turned democratic had they not been included in NATO—in exchange for gaining a crucial advantage over a despotic superpower with a history of aggressive expansion and a stated ideology of world domination.

Of course, the biggest example of this policy going wrong was American support of the Soviet Union during the Second World War, but there are plenty of reasons that doesn't get mentioned. Most people in my position would likely agree it was a mistake for the US to support Stalin as much as we did; if the Soviet Union came out of the Second World War in a much weaker geopolitical position due to a lack of food and industrial aid from the United States, the ensuing half-century would have been considerably better for the rest of the world.

The other reason it doesn't get mentioned is because your argument is a very old and worn-out Soviet propaganda talking point, and not only do Soviet apologists not want to admit that US support was vitally important to the Soviets during WWII, but they also don't want to admit that the Soviets themselves are the single worst autocratic regime that the US has ever allied itself with. Such an admission would underline the crucial importance of curbing Soviet domination over the rest of the world and justify exactly those actions that one seeks to criticize.