To answer the question one needs to define the terms. What does it mean to be a leftist, or right winger? Confusion on these terms lead many to embrace more laws and government intrusion in the name of liberty. Taking ten minutes to watch this little explication will be ten minutes well spent for the sake of clarity.
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and more:
http://suyts.wordpress.com/2013/06/19/shock-news-nazism-is-short-for-national-socialists/
Economics For Morons 
It’s clear that most people are clueless about fascism. I’m not sure how fascism ever got linked to the right. Although, it’s very easy for liberals because they associate extreme patriotism and racism with “right-wing” thinking. It’s only natural then that the Nazis with their parades and Antisemitism are considered right wing by those who are clueless about how fascism works.
I think it probably goes something like this:
It is evil to belong to the right
Hitler was evil
Hitler must have belonged to the right.
What many miss, and subconsciously hate BTW, is that Hitler embodies the end of their worldview. Killing jews and otherwise paving the way for evolution to usher in a “superman” race was a socially constructed “good” in Germany, and therefore moral. But leftist know better deep down. I think that’s probably why they are quick to glom onto things like “Godwin’s Law” which dissuades the mention of Hitler in discussions.
Leftists, love to win arguments through emotional statements and attacks. They label things in divisive ways that leave their victims speechless. Assessing Hitler’s belief in an all powerful strong arm government seems to lean more toward the left to me. He had no respect for the individual, supported abortion and other horrific medical experiments, confiscated guns and personal property, cheated at the polls, produced propaganda and slander toward the opposition, believed no tragedy should go unused, turned the education system into indoctrination centers, controlled the media, nationalized industry, attacked religion and built a system of corruption. He believed all rights came from the state, not from God. I just used an example of how leftists justify their arguments.
I’ve heard so many say he was on the political right. Again, such terms need to be defined. I ‘m not sure how leftist would make their case, but I’m sure it will involve a worldview based on make believe “truths”.