"The left" is an abstraction, there are only people on the left. And that includes philosophers, activists, the civil population, politicians, and institutions. These change in time and don't agree in every view.
But not a single author or political figure of the left has ever argued anything as exorbitantly stupid as "there are no differences between human beings."
The point is that the many differences between human beings, such as class, race, religion, gender do not imply a difference in dignity, and thus should not to generate inequality in opportunities or rights. This is why recognizing diversity is not contradictory with affirming equality.
That's what everyone, from Marx, to de Beauvior, to Luther King, to Mariátegui, to Bernie, means by equality.
Marx claims class difference ought to be abolished. Feminists that inequalities of opportunity and power based on gender ought to be overcome. Bernie that the oligarchic structure of governance generated massive inequalities of wealth and access to basic services like health care. And so on.
This is so obvious that the fact I have to spell it out to you is really shocking to me. That you are so outlandishly stupid to assume people are even stupider than you shows you live in a fantasy world. That you thought it was clever to bring this up is actually pathetic.
Read a fucking book, it's embarrassing for a functional adult to show this level of ignorance.