Alright. I will try to refute these arguments.
1. Class struggle does not encompass only the traditional white man working class. Class struggle is meant to encompass every worker regardless of their race, religion, sex, and ethnicity. A Black woman facing racial discrimination has to do something with the ruling class. Today, we have the capitalist DEI which encourages racism by hiring people based on their race. A Black woman will not feel secure even if there is a "representative" of the black people in the capitalist hierarchy. Therefore, capitalism can be racist for it aims to divide labor based on race. There is also gendered division of labor, as well as ethnic chauvinism, etc. The main problem is that libertarian socialists do not understand the mass potential of appealing to ALL workers and instead disregard the class struggle, claiming that it will lead to "totalitarianism". The whole New Left mindset is harmful rather than helpful. Therefore, class struggle must be considered the primary focus for as long as capitalism continues to deny any poor person the right to live a better life and move up, the class war must not be disregarded and there cannot be any compromise with the capitalist class.
2. Intersectionality is divisive and aims to disorganize the fight against capitalism. If we are to consider every form of oppression as "unique", then it defeats the whole purpose of revolution. The sectarianism of such "intersectionality" simply is incompatible with class struggle. Women fought for their rights not because "men are bad" but because the hierarchical system of such which also exists in capitalism is sexist. Women are paid less than men and capitalism would most certainly use a woman, not to "replace men" but to cheapen the labor and maximize their profit scheme. This is an inherently sexist example of how capitalism can exploit women and their labor, although the main disadvantage would be that women aren't as much physically good as men are due to biology but they can be used provided they are trained for it. Still, the aim is to reduce wages and increase surplus value, hence women would also band with men in the working class to fight off the capitalist system that is exploiting their labor based on gender.
3. It would be insidious to assume that every minority is fit best for their own. If that were the case, then socialism would have never happened and none of the great revolutions would have succeeded if every marginalized group prioritized their own individualist agenda instead of cooperation for capitalism is strong against loose networks but weak against a centralized and powerful agency. Would you claim that Black people didn't fight so they can be equal like everyone else but instead they want to be "special" unlike the others? Was the Civil Rights movement a failure because it did not prioritize its own agenda because it wanted to tell people that regardless of race, we're all humans?
4. Mainstream is indeed a problem that dominates the society. Here we can see the problem with gender roles for example. Marxism aims to abolish such, in a way that it will discourage the forced stereotyping of gender because gender itself is an identity. However, men and women still exist in a communist society because of their biology which should not be seen as an opportunity to divide labor by gender but instead appreciate the biological diversity of such. Unfortunately, many nowadays advocate for creation of multiple gender identities as a means of "rejecting social norms" which is inherently reactionary compared to what Marxism advocates for.
5. Marxism in the 19th century may have been mostly focused on the economic part but in the 21st century, Marxism also tends to focus on the social part. It connects both social and economic issues because the main enemy is still capitalism and who are the bourgeoisie at the top is not some "straight white dude" but also a diverse group of rich people who exploit others. There are indeed capitalists with a more divisive rhetoric (racism, sexism, fascism, etc.) but even the most "progressive" of the capitalists will exploit you no matter what! Social issues often arise from exploitation of the working class. You're born and want to be happy. You work hard and you do your best. But what's stopping you from success? An elite which is catered to reducing wages so it can maximize its surplus value against you. Whether that is domestic or international (exploiting third world countries).
6. Marxism certainly will respect such struggles and address their histories but it will also aim to unify the people regardless of race, sex, religion, and ethnicity. To not let people unite into a revolutionary socialist organization would be disastrous and would allow capitalism to win against the working class. Again, the working class is not represented by "straight white men" for Marxism now defines the working class to encompass anyone who has a low income and is being actively rid of their hard work by small wages due to capitalist profit motive.
7. Refer to numbers 2 and 3 for an explanation. Again, there is a correlation that black people are exploited by capitalism (Slavery in the United States) and that women are as well exploited by capitalism (smaller pay than men). These movements fight for equality, not for their own supremacy!
8. How can Marxism not change? Class struggle changed as well. To imply that it didn't is plain ignorance and denial of the importance of revolutionary change that helped transform societies into the better. Nowadays it is harder to overthrow capitalism but we must rely on uniting marginalized groups and banding them together against capitalism. If we can do this, then there will be another Great October Socialist Revolution to come.
Conclusion
The eight points provided are purely to justify the defeatist approach of the "Western Left", claiming that class struggle is "outdated" and that we must "compromise" with the rich elite. This is inherently dangerous to any new socialist or new leftist because it discourages them from being a leftist in the first place. This is the reason why the working class has mostly turned to the right-wing side of politics due to the ignorance of the Western leftists who are unwilling to appeal to the workers with an adequate Marxist rhetoric and instead parrot a corrupted neoliberal capitalist welfare agenda, calling anyone who is against their identity politics a "bigot" and "fascist".
(I couldn't use the quote because of the character limit, so original one goes to PTK)