For any entity x, if x “begins to exist,” then x has a cause.1 (Similarly, see every event has a cause. This is relevant, of course, because the Universe is an existing thing/entity.
C. D. Broad: “…I can not really believe in anything beginning to exist without being caused…. [I] find it impossible to give up the principle…” [“Kant’s Mathematical Antinomies”, Proceedings of the Aristotelian Society 55 (1955): 9-10.]).
By way of response, however, Craig needs to do more to defend this premise. After all, his analysis of "begins to exist" is a bit more metaphysically loaded than a premise like “every event has a cause”; Craig's premise not clearly what Broad had in mind in the quote above. To elaborate:
(a) Given Craig's analysis, the causal-principle depends on a controversial theory of temporal becoming called 'presentism'. The view is very intuitive, but it plausibly needs to be argued for more frequently since it is rejected by most scientists, in virtue of conflicting with the traditional 4-dimensionalist view of time (which is allegedly supported by Relativity theory). This has lead some philosophers like Graham Oppy to complain that we don't ‘intuit’ Craig's notion of “begin to exist” (See his Arguing about Gods(Cambridge, 2009), 150.) [Side-note: I suspect that most of Craig's debate proponents would have hammered Craig on this assumption if they had realized it was knit in to his analysis of begins-to-exist; I predict ithis will be a future source of criticism as the fact becomes more popularized.]
(b) Given Craig's analysis, the premise might also require defending Suarez's theory of causation, which is very controversial and not clearly intuitive (See Rutger philosopher Christopher Weaver's highlighting of this possible deficiency in Craig's argument here). If this argument does require a Suarezian theory of causation, then some might prefer a less demanding Kalam like this one.
If something can come from nothing, then non-existence can be “followed by” existence. This is relevant because non-existence being “followed by” existence is straightforwardly impossible.1