Commonly people say "if you have nothing to hide you have nothing to fear". Leaving side the origin of the phrase side, it is still a bad argument. You may not have something to hide now but can you trust that what you do now doesn't become something to hide? We've seen many times in history oppressive regimes rise out of free states. This power doesn't just belong to the government in the now, it also belongs to the government of the future. There is the possibility for turnkey tyranny. There's a balance to protecting the people now and people of the future (part of civil rights).

It belongs to other groups as well. We've seen pretty frequently the state of computer security in governments. Can you also trust that this technology won't be hijacked? Can you tell me that this system can't be used by an invading force to quickly target important individuals?

It isn't always what a technology is being used for that makes it concerning, you also have to consider how it can be abused. This type of technology, and most surveillance technology, has a high potential for abuse. By both our own governments AND adversarial groups.