Instead of emotionally reducing it to "don't kill grandma" you could join a reasonable discourse on the topic and look at other factors like...

The at-risk can get vaccinated - healthy youth don't get hospitalized - there are antibody and drug therapeutics available - youth don't need to risk novel vaccine adverse affects (they are documented - they are more prevalent in young than old) - you still spread it equally significantly vaccinated or not - the vaccine does not give robust coverage against new strains - natural immunity gives far more robust coverage against new strains than the vaccine (almost suggesting exposure for the low-risk is a better societal outcome).

Hand waving "all youth must get vaccinated" is not a rational course of action.