It's part of their never-ending effort to try to cast liberals as being "evil."
In the modern world, Hitler has become essentially a meme, denoting the personification of absolute evil. So, if one wants to claim that liberals are evil, then it makes sense (to those on the right) to claim that Hitler was a liberal or a socialist--the latter justified solely on the basis of the name of his party--complete, childish nonsense, of course, but that doesn't stop them...
Nobody in the 1930s and 1940s was under any delusion that the Nazis were socialists. They were widely associated with fascists, whom they resembled, and the Nazis themselves declared socialists their enemy, banning the German Social Democrat Party and Communist Party.
The claim that the Nazis are socialists is advanced today only by far-rightists who are determined to lie about 20th century history in order to disssociate their own racism and violent extremism from the tainted legacy of Nazism.
They have been enabled to do this by the spreading of the lie that socialism=strong central government of any kind whatsoever.
Socialism is about the ownership of the means of production, not about the power of government. In order to believe the absurd claim that socialism equals strong government, you have to erase from history the centuries-long tradition of left-wing anarchism and pretend that ‘libertarianism’ only belongs to the right. A belief in very strong government is authoritarianism, NOT socialism. Authoritarian beliefs are commonplace, even among those on the right who profess a belief in free-market economics.
It is an extreme and fraudulent form of historical revisionism to claim that the Nazis were, in any meaningful sense, socialist. If you’d called a Nazi ‘socialist’ to his face, he would have laughed incredulously, before calling on his buddies in brown shirts to beat you up for insulting him.
The Nazis were authoritarian nationalists of an extreme kind. This is why modern authoritarian nationalists (e.g. the most rabid Trump supporters) want to distance themselves from them.
There's two issues which come up a lot because apparently people can’t be bothered to read history books--
1) "The Nazis began as socialists!"
A.: The German Workers Party, forerunner of the NSDAP, did indeed have some anti-business elements in its party platform. These were retained in 1920, when the party renamed itself. The 1920 party platform (before Hitler had become party leader) included elements of the state taking over ownership of the land for state use, and the abolition of unearned incomes. Party membership was not open to all: members had to be of ‘pure Aryan descent’ and it was forbidden for members to have sexual relations with Jewish people. Socialism is supposed to be internationalist and class-based in nature, not defined by one’s ethnicity.
Hitler would not become undisputed leader of the party until 1925, in the wake of his imprisonment after the failed 1923 putsch. The other dominant figure in the party was Gregor Strasser, who was distinctly more left-wing than Hitler, calling for a rather incoherent economic revolution "maintained not by a soulless Jewish-materialist outlook but by the believing, sacrificial, and unselfish old German community sentiment, community purpose and economic feeling."
Strasser was very popular among northern German Nazis, Hitler more popular in the south. Hitler came to see him as a threat. In April 1930, Hitler explicitly dissociated himself from Strasser’s socialist ideas, and eventually forced Strasser out of the party. On June 30, 1934, on the so-called Night of the Long Knives, Strasser was arrested, along with all other members of the Party leadership that Hitler deemed undesirable. He was imprisoned, then taken out and shot. That was the end of the left wing of the Nazi Party.
2) "How can you say that the Nazis weren’t socialists? It’s in their name! National Socialist German Workers Party!"
A.: This argument is so childishly naive that it's almost unbelievable. The name of a political party, or political movement, is not a dictionary definition of the ideology of the party or movement. It’s more of a marketing tool, designed to attract voters. After failing to overthrow the government by force in 1923, Hitler had an epiphany while in prison--achieve power within the system by garnering votes. And he knew his party didn't have enough on its own--he needed to form coalitions with other competing parties, including the Social Democrats. He knew that once he was in power, he could throw any inconvenient "allies" under the bus, which is what he did. And once he was absolute ruler, what did it matter what the party was called? He was absolute dictator, it zll revolved around him, personally. He could have called the party, "Fluffy Pink Nordic Bunnies," for all it mattered. It was simply more expedient to leave it as it was--little reason to change the party name.
The Democratic People’s Republic of Korea is the official name of the country of North Korea. I don’t think anyone would agree that it’s actually democratic.
The Democratic Party, in the USA, was once the party of the slaveholders. This actually made sense at the time, since its original party platform was heavily based on the notion of ‘states’ rights’, particularly, the right to own slaves. But the idea that ‘democracy’ extended to slaves themselves was clearly not on the minds of the party’s founders.
The Conservative Party, in the UK, has historically claimed that its conservatism involves preserving beloved institutions and resisting radical change, but under Margaret Thatcher it didn’t hesitate to bring about radical change in the form of crushing the power of many labor unions and politicizing the Civil Service.
The name of the Irish political party Fianna Fáil means ‘Soldiers of Destiny’. For a party which spent much of its career being complacently pro-business, against change and generally non-militant, this is pretty funny.
The Greek political party, Golden Dawn is ultra-right-wing and aims to roll back liberalization in Greek society. ‘Iron Twilight’ would be a far more appropriate name. (Note that in the most recent Greek elections, GD lost all the gains they’d made).
The German Workers Party changed its name to the National Socialist German Workers Party in 1920, at a time of turmoil in the party. The word ‘Socialist’ was added to the name by the party’s executive committee, over Hitler’s objection, as a deliberate attempt to attract left-wing voters.
The Nazis were "socialist" in name only.