You're parsing it incorrectly. It can only be read that way in a literal manner that lacks all context. It is intended to mean "an injury to one (of us) is an injury to all (of us)" with the "us" being defined by the context in which it is repeated. In a solidarity context, that would be the exploited.

That's not really the position of the "old Left", a form that was far, far more succesful in uniting opposition btw - your "30 years ago" marks the beginning of a social coup by the right and a fragmented, weak opposition, the beginning of a gradual and unabated shift to the right across the whole spectrum of oppression and the intensification of oppression at a global level, even as the "new left" congratulated itself on superficial gains while bemoaning its newfound powerlessness in the face of a renewed and intensified assault against the populations of whole continents. The "New Left", with its focus on deconstructing offensive words and so on, has miserably failed the people of Africa, the Palestinians, Yugoslavians, Afghans and oh so many others. So weak is the approach that the right has even been able to manipulate things like anti-sexism and weaponize them in the service of oppression (a ploy that has been much exploited by proponents of the War on Terror), pitting one form of oppression against another. It has become nothing more than a philanthropist's club, a feelgood association for balming the conscience of well-heeled, affluent suburbanites. Given circumstances, I expect (and welcome) that the etiquette-based leftism embraced by soccer moms, spoiled university students, and men who wear it like a peacock's plumage is about to be rolled back into oblivion, and the left will be renewed and rejuvenated by exploited groups - with the strongest renewal probably emerging out of other parts of the world altogether, beyond the control of the affluent.

Economic oppression was viewed as a "mask", too. The reality being social relations between people.

For instance, this view would hold that it's a kind of magical thinking and fetishism to say that the racist does some racist thing because some entity called 'racism' compelled him to, and by making the appropriate penances, he can free himself from its influences - almost as if it were some sort of evil spirit. And if we all make the penances we can banish the evil spirit forever. 'Racism' is not an entity with agency - a trap much of the left has fallen into, in fetishizing the institutions of oppression and crediting them with an almost supernatural agency. All that exists in reality is social relations between individuals. These may be characterized as racist, sexist etc and we may speak of social relations being characterized by these behaviours and ideas, but they are still no more than social relations. There is no spirit of racism, animating racists everywhere. There is only a common theme to certain social relations between individuals, learned behaviours on the part of individuals.

In this particular case, we wish to marshal support to end the exploitation of prostitutes. I don't think your perspective can be very succesful in doing that, it's just going to turn people off. Imagine going up to a white prostitute who doesn't have a racist bone in her body and attempting to get her involved in anti-racism by telling her she's guilty of supporting it because she's white and she hasn't 'actioned' sufficiently to constitute the appropriate penance. What kind of response do you think you're going to get? A hostile one, and rightly so. Now imagine trying to get her involved by showing her that what she suffers, and what minorities suffer, is similar in many respects - appealing to her ability to relate her experiences with those of others. Which do you think is going to be the more succesful approach? The first doesn't make any sense at all to me. It is not only theoretically untenable, it is unworkable in practical terms. It is a complete departure from reality in every respect, and she would have every reason to be pissed off about it.

It's the same thing in getting people to support prostitutes. The best way to gather that support would be to talk about prostitutes in ways that people can relate to, not alienate people from them and then demand penance.