This is why I don't like locking doors exclusively for groups. This is why I removed the padlocked door for the sewer base.
People just aren't content with holding up in an abandoned building for some reason, and insist they have their own base. I guess I can understand this, because it makes you feel exclusive, but it really isn't needed.
My character, Peter, is a member of a small group of survivors and we've made home in an abandoned building and almost never get interrupted- we didn't and don't need an exclusive/special base.
If you want to make an area exclusive for yourself, just be aware there are other people in the server. I understand being territorial and trying to remain in-character, but at least try to remain courteous and aware that the other characters are actually being played by people, and you don't need to set out to ruin their experience.
Share the server. Having a shoot-on-sight doctrine doesn't add much to the roleplay.
I understand there are certain contexts or situations where doing this seems necessary, but make it clear to other roleplayers. If you make this clear then the other roleplayer has no reason to complain.
Not pointing any fingers here, by the way.
Also, for the whole getting around the blue door thing, I really don't care. It's not a bug or an exploit. That building is, quite simply, just more secure than the others.