Are you familiar with non-leftist thought? I've found when interacting with a lot of leftists that they became leftists first through their/others observations/feelings and then began to read leftist thought afterword, but aren't aware of how leftist thoughts fit into the general framework of political ideas. It makes it tough to discuss political thought with a lot of leftists because their only exposure to political critiques is through Marxist lenses, even though Marx himself was very well read in both philosophy and history.

Leftism and intersectionality is all about labelling folks into groups. Each person falls into an intersection of multiple groups (e.g. "African-American" and "presents female") and we can use this to have an understanding of their experience and the oppression that they face. Taken to absurdity, this reduces a person into a bundle of specific labels and doesn't make any distinction between the individual and their labels: well I'm a person of X race assigned Y gender born at Z time with immigrant parents who experienced A, B, and C event and therefore I feel Aleph oppression. The original critique was that, the "obsessive generalization" necessary to equalize the experiences of humanity paradoxically requires an obsessive amount of categorization.

> How is the idea of getting rid of class distinction "obsessive generalisation"?

There are many political philosophies that believe that some amount of class distinction is inherent to humanity. One can create a reductive 1D projection of political preferences by placing "classless, fully equal" society on the left as many leftist theories do and "hierarchical, predetermined classes for each individual" on the right as many fascist theories do. If you think that a "classless, fully equal" society is not extreme at all, then you're probably the one on the very left end of the spectrum.