As against such a view, I maintain that, in a fairly obvious sense, all goods are `up for grabs'. Obviously not all prior holdings are legitimate -- and so not everything a person has, or holds, or enjoys, is (legitimately, justly) his own (Flew himself implicitly recognizes that point). What a distributionist would then point out is that the needy's right to be treated so as to have their fulfilment as human beings enhanced overcomes or supersedes whatever purported `entitlements' have thus far been bestowed upon the small minority of the well-to-do -- and hence that none of the goods to be (re)distributed is due to those few people.
There may be degrees of legitimacy and of illegitimacy, so much so that some actions or holdings may be to some extent legitimate and yet up to a point illegitimate, owing to which a fresh redistribution of the goods thus held might be both to some extent just and to some extent unjust.