  Recall that Wykstra's principle requires that one have good reason for thinking x's would be apparent. Howard-Snyder's only requires that one not be in doubt, or perhaps, better, not have particular grounds for doubt, about their seeability. If some basic beliefs are prima facie justified, that is, justified until there is reason to doubt them, without explicit reasons, then skepticism will be more of a threat with Wykstra's epistemic principle than with Howard-Snyder's. Note that the truth of Obscurity will also work with Howard-Snyder's principle, so a defense of the parent analogy would also serve Howard-Snyder's case. 