having shkutzim as children, is an entirely separate problem and betrayal of Hashem, from marrying a shiksa.
I think it goes hand-in-hand. “Marrying” a sheigetz or shiksa (actually the “marriage” has no effect and they aren’t married – so essentially they are cohabiting) means they are doing the act that creates children. So the cohabitation and the having children, seem to me, are the same problem.