A couple of problems with your argument.That doesn’t seem too hard to understand. The Marxists were extreme anti-nationalists threatening a proletarian revolution to overthrow the government and take over businesses. Every advance made by socialists in terms of workers rights and better working conditions resulted in a better economy and a more satisfied population which was not acceptable to radical Marxists. They wanted a proletariat revolution not a satisfied population and national government, so they did everything they could to sabotage the gains, blame it on the government and continue to spread their anti nationalist propaganda and to agitate for a proletariat revolution.
They stirred anarchy in the streets and were destabilizing businesses. The government was unable to contain the anarchy.
First of all, the Nazis themselves were involved in the anarchy the German government failed to contain, with their own paramilitary (the SA) that fought the Communists in the streets. Hitler himself was arrested for the failed Beer Hall Putsch in Munich in 1923.
Secondly, while it is absolutely true that there were radical Marxist elements (like the KPD) who attempted to create a proletarian revolution in Germany, that doesn't describe the SPD, which was (and still is) a moderate social democractic party -- socialists who had successfully expanded workers rights and the welfare state through legislation prior to WWI. While the party officially became Marxist in 1891, they shifted away from revolutionary socialism during the early 20th Century and shifted towards legislative reforms.
The SPD were a part of the "Weimar Coalition" that met in Weimar in 1919 and were one of the principal parties that wrote the constitution for the Weimar Republic. They were considered rivals of the more radical KPD which did oppose the parliamentary system that the SPD helped design. Controversially, the SPD supported coalition that put down the far left Spartacist uprising in 1919 that led to the murders of Karl Liebknecht and Rosa Luxemburg.
The Iron Front -- an independent paramilitary opposed to both left and right-wing totalitarian ideologies -- was largely run by members of the SPD, even though no formal relationship existed.
Below is an SPD election poster from 1932, urging the population to vote for the social democrats in order to oppose the monarchists, the Nazis and the Communists.
![Image](https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Three_Arrows_election_poster_of_the_Social_Democratic_Party_of_Germany%2C_1932_-_Gegen_Papen%2C_Hitler%2C_Th%C3%A4lmann.png/512px-Three_Arrows_election_poster_of_the_Social_Democratic_Party_of_Germany%2C_1932_-_Gegen_Papen%2C_Hitler%2C_Th%C3%A4lmann.png)
In 1933, when the Reichstag banned all parties except the Nazis, the SPD were the second largest party in the parliament. The Nazis partnered with conservative parties in order to get the 2/3 majority to pass this legislation.
So while I agree that anti-Communism and socialism was part of what motivated the coalition between the Nazis and German conservatives, that was not the sole motivation. There was also ideological agreement.