That's too strong a claim and doesn't factor akrasia in; you might as well say that you don't really believe in the seriousness of existential risks if you don't spend every waking moment working against them. [...]

Okay, fair point. My claim was too strong and I accept your modification. Still, existential risks still permit me finite remaining life, which still keeps its utility very very far from that of eternal torture espoused by some religions.