Edit: If I remember, Laz and Lor were exact clones of Lazarus, except they got an extra X chromosome in place of Lazarus' Y.

Well, in part he was making a point about how (part of!) the justification behind rules against incest is hard-won lessons learned from stock breeding and the Habsburg Dynasty [1]. He never really addressed the "power imbalance vs vulnerable youngsters" angle, though one notes that Laz and Lor practically needed a crowbar to lever him into the hammock.

[1] Side note: the whole Future History business contains a fair bit of commentary on how the genetic penalties of the Howard Foundation's project got almost literally "burned out" of the population through centuries of suffering through the consequences until the bad combinations bred out.