I don't agree with them. Vaccination does help prevent transmission, since it reduces the risk of being infected in the first place, and if you're not infected, you're not infectious. Additionally, Covid-19 itself has a substantially higher risk of myocarditis, and that also tends to present itself more seriously than the rarer vaccine-associated myocarditis.
So, assuming the risk of exposure to Covid is substantial, then vaccination offers an overall reduction in the risk, and potential severity, of myocarditis. Plus the indications are that it reduces the risk, and severity, of long Covid, etc.