The risk of dying or long-term complications from COVID if you're under 50 is not insignificant, especially on the upper end. Here's a pretty good graph of the estimated IFR by age [1]. (So far, there hasn't been a significant difference in lethality in the new strains).

The graph shows about a .1% chance of death at age 50 if you catch COVID-19. The chance of hospitalization and potential long-term symptoms is a multiple of that.

Vaccinated folks have a lower chance of catching COVID, so as a whole, they have a lower chance of spreading it.

1. https://pubmed.ncbi.nlm.nih.gov/33289900/#&gid=article-figur...