Marx and the Irish Referendum

The Irish Times has chosen to quote Karl Marx in regards to the same-gender marriage referendum.

Humans are not equal in their endowments or talents. Some are stronger physically or mentally, or more experienced emotionally, than others. What they have in common is their differences and their ability to express them individually. If you treat them the same, you will therefore do them an injustice.
This contradictory aspect of equality led Karl Marx to argue, when criticising the Gotha programme adopted by the German Workers Party in 1875, that the equal rights it proclaimed were in fact constrained by their emergence in a capitalist society.
That equal standard or right “is in fact an unequal right for unequal labour . . . It is, therefore, a right of inequality, in its content, like every right.”
He went on to say that only in a much more developed phase of communist society would it be possible to cross out this narrow horizon and substitute a principle fully recognising these differentiations: “From each according to his ability to each according to his needs!”…
…. If the amendment is passed, we will have moved away from a position in which equal too often meant identical to a more genuinely pluralist one recognising human difference as a foundation stone of political and social equality.