Thanks @iwontsignuphere @jkphl.
Switching Twitter to public for #MozLondon.
Note: problem of nonsense replies still exists, public or private.
Twitter has no mechanism for deleting (or at least disconnecting/hiding) nonsense (or abusive) replies to your tweets, on your tweet permalink pages, e.g. the replies after @iwontsignuphere @jkphl to this thread:
https://twitter.com/t/status/742610971181469696
Even if I block senders, they still show up for everyone else viewing that tweet permalink.