The response to this, of course, will be "well the risks of the virus are still higher than those of the vaccine so you should still get it," but I think that misses an important point here. In the absence of long-term safety data on these vaccines, we have engaged in a priori deduction instead: "there's no known mechanism by which mRNA could cause any complications, so it should be fine." The appearance of any significantly higher than expected rate of complications potentially calls that reasoning into question.