Why is Communism singled out as a totalitarian party in US immigration laws?

Question

US Immigration laws state

(D)Immigrant membership in totalitarian party

(i)In general

Any immigrant who is or has been a member of or affiliated with the Communist or any other totalitarian party (or subdivision or affiliate thereof), domestic or foreign, is inadmissible.

Why is Communism singled out? There are many parties that someone can perceive as "totalitarian" (it depends on the country and on the individual) but only Communism is noted.

Are all Communist parties seen as being the same (there is a huge difference between, say, the French Communist party and the North Korean one)

Answer 1

The restrictions you're interested in were introduced in the 1950s, during the Second Red Scare. During this period, there was growing concern that "international communism" was intent on infiltrating and subverting the government and society of the United States.

The main acts in question were the Internal Security Act of 1950 and the Immigration and Nationality Act of 1952. The USCIS Policy Manual has some information on the history of these restrictions:

The Internal Security Act of 1950 also amended the Immigration Act of 1918 by adding new grounds of exclusion specific to members of communist or totalitarian parties, affiliates of such groups, or to noncitizens who advocate the doctrines of world communism or any other form of totalitarianism. It likewise expanded the deportation provisions to cover such noncitizens.

...

Subsequently, Congress passed the Immigration and Nationality Act (INA) of 1952 which, for the first time, authorized the exclusion of all noncitizens, immigrants or nonimmigrants, on the basis of membership in or affiliation with the Communist or any other totalitarian party. As with previous acts, the INA of 1952 also declared that noncitizens were excludable based on a wide variety of other activities linked to the Communist Party or other totalitarian parties even if the noncitizens were not members or affiliates.

As to the question of why the law painted all Communist parties with the same brush: up until the early 1950s, there was substantial coordination between the Communist parties of various nations, with (at least originally) the stated goal of "the overthrow of the international bourgeoisie and the creation of an international Soviet republic as a transition stage to the complete abolition of the state." So at the time, there was less difference between the policies of various Communist countries than there is today. The death of Stalin and the rise of Mao eventually led to the Sino-Soviet split and more differentiation between the policies of various Communist parties; but that was still in the future when these laws were passed.

Answer 2

Communism is a totalitarian ideology - advocating for suppression of individual freedoms in the name of common good (aka in the name of "people"). One may agree or disagree whether it is a good idea, but it is not consistent with liberal democracy practiced in most western countries.

To add material from comments:
what is singled out is not how party is perceived (as the OP suggests), but the ideology it represents. A party that has "communism" in its name cannot pretend that it has nothing to do with the works of Marx, just like a party that calls itself fascist or national-socialiste cannot claim that it is unrelated to its infamous historical predecessors.

Update

Why is Communism singled out?

Communism is not singled out - rather it is cited as an obvious and notorious example of totalitarian ideology, the primary target of the law. The clause or any other totalitarian party is added for inclusivity, to account for more obscure or yet unknown ideologies (fascist and national-socialism had been dealt separately a decade or two earlier.)

Are all Communist parties seen as being the same (there is a huge difference between, say, the French Communist party and the North Korean one)

As I pointed out above all the communist parties follow the same ideology. Contrary to laymen opinion, communist parties in 50s were not just political parties like all others - these were paramilitary organizations, aiming at clandestine preparation of a revolution (i.e., overthrow of the existing political order), subject to the strict party discipline, and to orders from Moscow (nor simply financial support). Thus, La Partie Communist Française, mentioned as an example, refused to condemn the German invasion of Poland in 1939, continued to blame the war in the "British and French imperialism" even in 1940, when the Paris was occupied by Germans, and praised Marechal Pétain for concluding the armistice - for during this period Nazi Germany was tied to the USSR by the non-aggression Molotov-Ribbentrop agreement, and the party was directed to support the Soviet line. Only after the German attack on the Soviet Union did the party join La Résistance, becoming a leading force in it - partly because it had already developed paramilitary and command structure and partly, because de Gaulle allowed it to take the leading place in exchange for the Stalin's support for his leadership (unlike various governments in exile residing at the time in London, de Gaulle did not officially represent any government, and there were alternative candidates for leading French, notably General Giraud.)