those things which do not exist, but those which are potential, and
not actual. For goodness has the aspect of the end, in which not only
actual things find their completion, but also towards which tend even
those things which are not actual, but merely potential. Now being
implies the habitude of a formal cause only, either inherent or
exemplar; and its causality does not extend save to those things which
are actual.

Reply Obj. 3: Non-being is desirable, not of itself, but only
relatively--i.e. inasmuch as the removal of an evil, which can only
be removed by non-being, is desirable. Now the removal of an evil
cannot be desirable, except so far as this evil deprives a thing of
some being. Therefore being is desirable of itself; and non-being only
relatively, inasmuch as one seeks some mode of being of which one
cannot bear to be deprived; thus even non-being can be spoken of as
relatively good.

Reply Obj. 4: Life, wisdom, and the like, are desirable only
so far as they are actual. Hence, in each one of them some sort of
being is desired. And thus nothing can be desired except being; and
consequently nothing is good except being.
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THIRD ARTICLE [I, Q. 5, Art. 3]

Whether Every Being Is Good?

Objection 1: It seems that not every being is good. For goodness is
something superadded to being, as is clear from A. 1. But whatever is
added to being limits it; as substance, quantity, quality, etc.