Again, we are talking about introducing something that is guaranteed to be in your body anyway if you contract COVID-19. SARS-CoV-2 is viral to the point where, without perpetual lockdowns/mask-wearing/vaccinations, you will get it. So it is still definitely better to get vaccinated, at least with an mRNA vaccine – please stop spreading FUD. Your concerns could be more warranted for vaccines like J&J which use modified viral vectors, but again, exceedingly unlikely that this could be any worse than the virus itself.
To open up again we need to bring the demand on healthcare services down and we need to do it sustainably, i.e. in a way which prevents another exponential spike. If we can achieve that aim without mass vaccination of healthy young people then great, of course, let's do that. But: if the only way to squash this thing and return everyone to a somewhat normal life turns out to be to keep vaccinating until we get right down to the twenty year olds, shouldn't we do so -- for their sake as much as everyone else's?
The mRNA in the vaccine lasts a matter hours.