You've got me there. It is indeed a mystery why the 'Brions continue to place such slaves within their castles, if they wish to keep us out. However, exiles often enter the 'Brions' keeps for other purposes, as "hunting" and "exploration." Unfortunately, exiles often take the "kill first, ask questions later" approach to exploring.
If you leave the doors to your house open, then don't be surprised when people come in and make themselves at home. Furthermore, the more we explore the more slaves we find that are put there to interact with us. Such as the new ruby necklace we can make with items found in the mines and keep of Melabrion.
As to the "kill first, ask questions later" approach, part of it is the way the world works. If we can kill something, it can probably kill us so when you see a monster approach you and, instead of talking, it tries to rip your throat out what would your first reaction be? Well, you might decide to run or if you're with a sizeable party you might defend yourself by killing it first. It might be unfortunate but that's how the world works.
Yei, these creatures were indeed created by the 'Brions. Melabrion created the Mud Golems, Tenebrion the undine, and Umbrion the Lava Beetles and Lava Walkers. Did you think that they just happened to appear in the 'Brions keeps?
While Mud Golems did first appear in Melabrion's Keep (to my knowledge), the others were around long before any of the Brions appeared. So the Brions would have had to create these beasts since before the Ripture War while hiding their existence from exiles. Do you have any proof of this or do you just say this because these beasts show up in the Brions keeps?
What interesting logic!
I believe that it was correct logic.
"If exiles don't want Darshak in Puddleby they can close and lock the gates so they can't get in. Since the doors to the town are open, many assume that it means they can go in."
"Therefore, if the exiles of Puddleby are upset at the Darshak for any of these acts they only have themselves to blame since there are several actions they can take to remedy them."
This is correct. If exiles were upset at the many invasions, we should create a set of walls/doors which can be quickly erected at the first news of an invasion. Combine that with long-distance weaponry or the means for exiles to quickly leave town through another method (such as underground) so that we can hit the invasion from their back or flank while they try to breach the defenses and get into Puddleby. This would ensure that those within Puddleby are safe (or at least until the defensive walls are broken) while enabling those able to defeat the enemies to do so. In fact, cadders could even be within the walls and cad the fallen/injured without risk to themselves. This hasn't been done because no creature has really been able to destroy our buildings or enter them so our tactic of using the libraries to heal the wounded and fight in town center has worked so far. Plus, the only beasts that wander into town are vermine, rats, and myrms which are more of a nuisance than anything else.
The point still remains, if exiles are unhappy at invasions then there are certainly many things we could do to stop them. It might take a while and a lot of material but it's certainly doable.
Did you really think I would take one approach to how the Brions should view their private property and another with exiles? That would be hypocritical and illogical of me to say the very least.