Why is it legal to photo or videotape celebs, but....?

I was wondering about the laws of privacy, or lack there of, and when it comes to photos or videotapes of people in public, or private settings. For example, its ok to photo celebrities while they're on a beach on vacation, or getting coffee at the local java joint, and plaster them all over the internet, TV, and magazines.

But! When you see other programs on TV, the bystanders are often blurred out, usually because they did not sign a permission waiver to allow them to be shown.

So, where is the descrepancy here, what is the law, and why do some people get to be blurred out, while others are "fair game".

In my opinion, it should be illegal to stalk people and sneak shots in when they are in public, unless they give permission. This is harrassment, it should be against some kind of privacy law, or one should be written if there aren't any common sense laws in place. Think of how many hundreds or even thousands of frivilous lawsuits happened because this problem, and how many wasted tax dollars and courthouse time has been wasted.