Requiring vaccination or proof of recovery is, for the young segment of the population, primarily not about reducing deaths at individual level, but at societal level as the occurence of breakthrough infections is much lower in the fully vaccinated population.
Whether such a mandate is ethical is another question. I'd much rather have governments make more of an effort to convince people to take vaccination without forcing them, and combat misinformation without resorting to censorship.
As for avoiding costs of PCR tests: maybe unvaccinated could resort to organizing and attending 'covid parties' in order to get infected with and recover from Covid? Parents of young children have done similar things with regards to some infectious childhood diseases for a long time.