i think the problem is it's a highly technical, mathematical and social problem that isn't easily explained. well, the technical part is even comparatively simple. but the negative implications are usually harder to communicate. the "slippery slope" argument only gets one so far and non-criminals usually can't imagine how it would negatively affect them. "only metadata" doesn't sound too bad!

the opponents of full encryption though have it quite easy by name-dropping the FUD buzzwords - i.e. security and terrorism. and anyway, it's only metadata!