Here's your mistake, and the mistake of everyone who thinks the way you do:
You cherry-pick examples of abuse -- and that's exactly what it is, illegal abuse -- and extrapolate it, in your mind, to being a systemic problem. You imagine it's happening all the time, and that people just sit around at their desks looking up their friends, girlfriends, neighbors, and ex-spouses for fun.
You then cherry-pick completely unrelated, long-ago-condemned examples of things that happened decades ago under the Hoover FBI, which is about 180 degrees opposite from what NSA does for foreign intelligence, and before there was any semblance of anything that could remotely be called intel oversight, and pretend it's exactly the same.
Your mistake is that you think isolated examples of abuse are not isolated, without proof; then you believe that any such examples indicate what, to you, is obviously a systemic, widespread problem. Abuse will ALWAYS happen, and it will never stop. This is true at all levels of government, and anywhere a human being exists. The answer to that is oversight (something you also think doesn't exist, but is actually so overbearing and restrictive that if you could actually witness it, you wouldn't believe it), not removing any authority that "could" be abused, because then we would necessarily have to remove them all.
Yes, intentional abuse, unintentional abuse, simple mistakes, human or machine error, and all manner of things happen in intelligence work. And those errors are such a vanishingly small proportion of what NSA does that it is nearly zero -- and they are still taken seriously. In fact, this is one of the single most important things drilled into anyone doing foreign SIGINT, military or civilian, every single day. It's not some kind of a joke.
I hate to break it to you, but how things actually work might disappoint you if you think there is rampant abuse everywhere.