Alright, don't worry about being annoying. My fault for not providing enough info. Like I said, I wrote this up when I was still relatively new.
Here's kind of how it works:
Upon construction, Defenders are more like "mindless machines that don't quite have a directive" and only basic programming until the mind of a human is linked up with theirs via transplant (or other various ways). Humans come in and their minds are linked, allowing the information Defender's need to flesh out their own programming and personalities, understanding, etc. It's sort of like self programming, but their own CPU's aren't quite large enough to house their entire program, thus a human acts sort of like a secondary control system. If any of that makes sense. They sort of become one, but not really because they're still their own individuals.
Since humans aren't as physically powerful as a Defender, they usually do stay within a Defender Compound, which is where most Defenders spend their time when not in battle, as shutting them down entirely takes up time--but it does happen when power reserves in the Compound are low. Since most of the humans stay within the compound, they usually take it upon themselves to debrief their Defender. If a bond is particularly strong between a human and Defender, then the human can go out into battle with them, but not many do this because it still requires augmentation beyond what they already have.
Defender's don't have many rights, no. The main Earth population doesn't think of them as citizens, just weapons. Defenders are somewhat okay with this, but problems have come up in the past when it came to their treatment. While a Defender could easily take down the entire Earth government, their most base moral programming would either shut them down or try to convince them otherwise. Most want this program gone, but humans (excluding the Defender's human link) disagree.
That got long, but I'm trying to get this to make sense. Let me know if there's anything else you would like to know. I'm still kind of building upon the whole thing and looking for input.
Edit: As I've said before, Explorers are pretty old in comparison, with more time put into their design. They have full capacity to develop their personality on their own.