1. it fails to address their actual argument, which is that they have nothing to hide from companies or the government, especially law enforcement.
2. it fails to convey the actual threat of loss of privacy: the threat to democracy and freedom of speech when journalists can't protect their sources, lawyers can't be trusted by their clients, etc.
I therefore prefer to emphasise that latter point, that even though they might have nothing to hide, people they should care about do.
Although lately it's become easier to convince people that even they have something to hide: as political actors (e.g. Cambridge Analytica) learn more about them from their data, they can target you (and people like you) with tailor-made lies to influence who you (and people like you) vote for.
Doesn't convince or even interest everyone, of course, but more than before.