Full Idea
Marx rejected the idea of equal rights, not because he was not a friend to the idea of treating people as equals, but precisely because he thought rights failed to live up to that ideal.
Gist of Idea
Marx rejected equal rights because they never actually treat people as equals
Source
report of Karl Marx (works [1860]) by Will Kymlicka - Contemporary Political Philosophy (1st edn) 5.1
Book Reference
Kymlicka,Will: 'Contemporary Political Philosophy (1st edn)' [OUP 1992], p.163
A Reaction
Presumably because the power to award 'rights' goes to the highest bidder. If equality is to be enshrined in law, it is a bit difficult to see how else to manage it.