First, the data is accessible by credit card provider, but also by several financial and technical intermediaries. Second, there is no way for any of those companies to guarantee that the data will never be leaked.

Then, in terms of consequences, it includes reputional risks, security risks people know your behavior patterns, and to be arrested for being at the wrong place and wrong time. Then is all the track record of governmental overreach that used this type of data, from arresting environmental activists to killings based on sexuality (for example). It happened in everywhere, and it still happens today.