In the same vein, with my family I've been using the analogy of "Imagine that all law enforcement had a key to your home, and they could enter at any time and look through your things, but you wouldn't even know it if they did, or if they took photos or recorded videos of your place to take with them. Their argument is that the only way to keep you and your stuff safe from the bad guys is for the good guys to have access. But because the good guys now have access, it's also easier for the bad guys to get in, because now there's all these extra keys to your home out there, which might fall into the hands of the bad guys."

Not a perfect analogy, but it seems to make them consider the issue from a more personal angle. And for those that argue, "Well, I don't have anything to hide.", I usually counter with "Then why do you close your curtains/blinds when you change your clothes or get out of the shower?" With my dad who grew up during the World War II, it also helped to mention that a law like this, once on the books, will not be easy to overturn, and while he might be fine with our current regime having access to all his data, that might not be the case with future authorities.