I share your skepticism. Vaccines are a relatively new technology, with various buggy vaccines coming out that were actually more harmful than helpful. Time will tell if the mRNA "Vaccine" will be a net positive. I am totally okay with other people injecting whatever they want in their bodies, as long as they don't try to make me do it, too. I would rather die of natural causes than a rushed-to-market product.
What do you mean "Vaccines are a relatively new technology"?
We've had vaccines since 1796 [0] when Edward Jenner developed a vaccine for smallpox, a terrible disease that we fully eradicated thanks to vaccination. A disease that you and me don't have to worry about because of vaccines.
(Likewise for Cholera, Tetanus, Polio, Tuberculosis, Meningitis, etc)
Also, trains, cars, planes, cameras, lightbulbs and every invention of Edison are newer technologies than vaccines.
Maybe they mean "mRNA vaccines"? COVID vaccine is the first of this kind, so some side effects, especially long term ones, are still unknown. It's still unlikely that they would be very serious but we won't know for sure until 10 years from now.