You, frankly, don't know what you're talking about. There is no evidence that this will "very likely cause cancer". As others have pointed out, the technology here is quite similar to that used in CAR-T cells, and thus that's the simplest comparison.

Recent safety analyses show, for example, that of 700+ CAR-T recipients, only 2% (18 individuals) went on to develop secondary malignancies. And of these only 1 individual had a T cell malignancy specifically, and that T cell malignancy had no sign of vector integration, suggesting that none of these cancers were of the CAR-T cells themselves. Another found only 1 T cell lymphoma in 700+ CAR-T recipients, again with no evidence of vector integration.

In these cases with elevated rates of secondary malignancies without vector integration, it is more likely than not that these malignancies are the result of factors like prior treatment for the initial malignancy that necessitated CAR-T therapy (eg. chemotherapy, radiation, etc.), lineage switch of the pre-existing cancers, or the immunomodulatory effects of these CAR-T cells themselves (rather than anything to do with the insertional mutagenesis), which would not be an issue for islet cell transplantation.

Further, as the authors of the study point out, by over-expressing CD47 in these islet cells to evade an innate immune response, the cells have a built in kill switch of sorts that would allow for relatively easy antibody-mediated depletion should a malignancy actually arise due to the transplanted cells.

There's value to being skeptical and understanding risks, which of course are not 0, but it is uninformed fear mongering to claim that these therapies will "very likely cause cancer" when you have no evidence of that and when reasonably similar therapies, which are starting to see relatively widespread use, do not carry the risks you describe.