I've laid out the counter-arguments to your post in comments here and here.
Suffice to say, in addition to those comments that a hard fork to advert the theft of multi-millions of dollars of ETH, is warranted as (from what I understand) the hard fork will only adversely affect (in a major way) the perpetrator.
The difference between this recursive split attack and MtGox is that, in this attack the stolen funds are contained in an identifiable account and will be sitting there for a few weeks. There is time to remedy the matter without affecting the fungibility of ETH. The DAO/ Ethereum team should thank their lucky stars and fix it.
If they don't fix it, they leave themselves open to legal claims that they had a fiduciary duty to recover the stolen money, yet choose to do nothing. I think this case has more legs than any claim the so-called attacker could bring.
I think the issue is the money wasn't stolen, the attacker saw a loophole and used it, it's shitty but it's like if a store was giving coupons giving you a free orange and then you get lots of coupons and clean the store out of oranges.
The store owner might say, I meant to write "one per customer", then you say "should've, but didn't".
In your comments you mostly focus on courts. A perspective which in my view is not relevant. I believe the whole point of Ethereum is to osbolete courts by having code excecute law. Whatever happens in a court has no bearing on what Ethereum should or should not be.
Keep in mind that TheDAO, even though it raised fantastic amounts of money, is just an app on Ethereum. Ethereum (the platform) shouldn't be responsible for bugs in every app running on the platform.
If Ethereum shows that it can make arbitrary changes to history, initiated by consideration of special interests, that will undermine the neutrality and immutability of the platform. It would basically make Ethereum untrusted and less valuable.
There is a big difference between what "should be" and what "is".
Code does not execute 'law', it executes the whatever the coder coded. Hopefully if they are a good coder it executes what they intended to code. Wishing the courts were obsolete does not make them disappear.
You're right, on one level The DAO is just an app on Ethereum. However the same people play a prominent role in both entities. Which is why it is Vitalik and co trying to convince everyone to fork. No fork = potential massive law suit. This is what 'is'.
I hear a lot of talk about blockchains being "neutral" and "immutable". I don't see it. They can be (and are) forked based on consensus. They are not 'trustless' because users 'trust' that the majority of miners will act only in the interest of the protocol. Even deciding what is in the 'interest of the protocol' is subjective, see for example the Bitcoin block-size debate. This is an inherent 'weakness' (or strength depending on your view point) of ALL blockchains.