Their reasoning behind that way of thinking is that they aren't wealthy enough to become a victim of theft and whatnot. They don't realize how stupid they make themselves look by talking this level of nonsense.
I kind of understand the general apathy towards their own data. They simply don't know any better regarding the potential risks, and it's hard to blame them considering how new all of this internet boom is -- it hasn't even lasted one generation. The concept of protecting your online privacy hasn't even reached the mainstream until a few years ago. Things are starting to change, with websites being open about their privacy policies, etc. so people are bound to wise up as we go along. But yeah, the "nothing to hide nothing to fear" mentality is just stupid.
That being said, I guess it just boils down to trust for those who are informed. I have nothing against sharing your data for as long as you know the potential risks. I just find it funny that people seem to feel like they don't have a choice with KYC, like exchanges are absolutely necessary.
Yeah absolutely there is a risk if you divulge your personal information, your personal identity, but for the trading site who will ask your KYC will be held responsible of all the information given by their patrons, in the world of cryptocurrency trust is the essential things.