> So far there's zero evidence these things being used illegally domestically.

There is evidence that NSA employees or contractors have used domestic surveillance to spy on exes. There is evidence that Marines have shared clandestinely obtained nudie pics of female Marines. Why would the people working at the CIA be any different?

If you take a large human organization, and give them the tools to spy on their fellow citizens, it is likely that those tools will be misused by some people in that organization.