I haven't found decades of positive result studies with mRNA...you might have sources you can share. Articles from 2017 show that Moderna was failing with mRNA and was close to abandoning it. Another journal article from March of 2019 stated that "Although mRNA vaccine technology has still not extensively tested in humans, publications of preclinical and early clinical tests have emerged in recent years, in which promising results were reported."Front. Immunol., 27 March 2019.
Again, there are people who are going to be comfortable with the amount of testing or believe the potential benefit outweighs the risk. That is fine. It is also not unreasonable at all to feel that more testing needs to be done and mandating a vaccine that hasn't been tested in the same way that others have is a big issue. I trust my immune system at this point.