[ujki1]

That statement could mean at least two things.

If someone doesn't care about his own privacy (but avoids endangering others' privacy when sharing information about himself), then that's his personal decision. One can list some of the possible but unlikely negative consequences that the person might not have thought of, but they aren't very strong counterarguments.

If the statement means "violating everyone's privacy is ok because I've got nothing to hide", then the counterargument is that some people legitimately have something to hide.