@r_alb time is the enemy: if you don't have privacy now, someone in the future can use it against you later. Let's say I am totally, 100% happy with the government of my country. I support some slightly controversial causes but I live in a democracy and I have a right to my opinions. In 10 years' time another government gets in and it turns out that support for legalising cannabis is support for drug barons, who are now defined as terrorists. Oops!
Orrrr I get tested for HIV as part of a visa requirement (multiple times). Obviously I trust the health service! Later on as part of a public/private partnership this information gets shared with my health insurer. They conclude that my lifestyle is riskier and hence costlier than it actually is. Oops!
It's not really about who you trust now, it's about having a reckless amount of trust in the future.