This. The thieves guild is not in it to help others, they are there to help themselves. They are not an evil organization trying to screw everyone over, but nor are they some charity band of men in tights.
In lore the thieves guild has little to do with Nocturnal, and their origins next to nothing. It's implied the guild existed before the Gray Fox stole the cowl of Nocturnal, and the only thing really connecting that Daedric prince to the guild is the member's respect of her and her domain (shadow hide you). In Oblivion the reason the beggars were under the protection of the Gray Fox was because they had a business arrangement: they would not be stolen from, and in exchange would work as the eyes and ears of the guild.
If anything, the Thieves Guild should only be in it for the money, or for personal glory and the continued existence of the guild. Keep it morally gray.
I underlined what I disagree about of what you said. I agree with the rest.
The beggars in Oblivion weren't under protection of the Gray Fox because they wouldn't be stolen from. I mean... they are beggars, they have pretty much nothing, so there's nothing to steal.
The beggars were instead proteted because they would be given things, like... gold, food, etc, in exchange for information. So it's kind of the opposite of what you said. They would be given things, not stolen, in exchange for information.
I just had to mention it when I read what you said, because it's pretty important. The idea of this Robin Hood thing isn't a bad thing by itself. But it was overdone in Oblivion.
Personally, I kind of want a mix of all three poll options, but with "honor and respect amongst thieves (Godfather)" as the main thing to focus on. Most thieves should stick to the honor amongst thieves.
A few thieves could be really gold-hungry and be scoundrels, and sometimes break the honor of thieves.
A few thieves could, once in a while, give gold or food to beggars in exchange for infromation.