I don't really deeply feel that anyone needs an airtight reason for quoting from the works of the writers he loves, but it's always nice, I'll grant you, if he has one.
Why do croutons come in airtight packages? It's just stale bread to begin with.
The way I was brought up ‘he needed killing’ is an airtight alibi.
Being dead is the most airtight defense of one's own aesthetic.