Interesting. Where/when are they not opposed?

Edit: Noting that I didn't mean that they are mutually exclusive outside of social structure.. You can take individual actions in a socialist society. The question is just around which is the core principle of the organisation of society.

Edit 2: to me anarchy isn't inherently individualistic, it is just opposed to power-over social structures. You can have a voluntary socialism. Look at Chiapas, for instance.