For those who argue that Marx did not advocate a “workers’ state” similar to Leninist conception, but rather something more closer to a “workers’ federation,” which I don’t believe, I think it is important to understand that social democracy does not conform to whatever conception Marx had in mind. So, yes, you can attempt to find a libertarian interpretation of Marx all you want. But that doesn’t change the nature of social democracy, which was not even invented by Marx.
The reason why it is called social democracy, or more accurately socialist democracy, is that it is a movement aspiring to create a different form of democratic government, of a state that manages capitalist class society. The term “democracy” implies a type of government, of a state.
But the democratic government desired by social democrats is also a socialist government, one which, by popular mandate, work towards the creation of a socialist society. As anyone who is familiar with my posts, I don’t think this is a viable method to achieve any form of socialism. And I also do not think it can come in libertarian form, or that the vast majority of social democrats, historically, would argue that it can or should be libertarian.
Thus far, I am stating the obvious. If Marx had something else in mind, which is not plausible, then you really shouldn’t call yourself a social democrat or keep on defending that term by constantly referring to what Marx and Engels wrote or said.