Because companies have already tested it for safety during clinical trials, and the FDA approved it as a result (in the U.S.). MRNA technology isn't exactly new either.
Aaand the amount of side effects reported are really rare. If it was really an issue, we would be hearing about it a whole lot more. In U.S. alone, we have at least 150 million take it, and how many reports of side effects and long term damage? Maybe a few hundred at the most?
Compare that to risking getting covid where the side effects are way worse.97% of the hospitalizations and deaths now are from being unvaccinated. And even if you don't die, you can still get long term damage to your organs like scarring or from blood clots. Might make men impotent and it could affect your brain as well.
I think these are all solid arguments.
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"The Dragon Ball Super anime is lowering the IQ of the characters so the DB fan base can relate to them better." -Acharyap28