In the past, Wikileaks has not been the moral arbiter. If a whistleblower decides that exposing information is in the public interest, that is on them, Wikileaks provides a medium.
Here, whether or not information should remain secret, there is an incentive to expose it. Wikileaks has decided what deserves to be public -- it's irrelevant if I, personally, agree with that judgment when I say: this makes me question Wikileaks as a trusted medium.
Considering that Wikileaks exists to make conspiracies harder/smaller I think this totally fits with their purpose. The only question being why it applies to this, but not to other leaks.
Really, the TPP should be public, shouldn't we be questioning the trust of the Governments?
But it should be acknowledged that Daniel Domscheit-Berg 'stole' 5GB of Bank of America documents from Wikileaks servers as well as their submission system, which he used to launch openleaks.
So you can definitely question their internal security, but it should not be presented as an affirmative decision on the part of the organization.
Thought experiment: if governments knew that any decision made had a chance of becoming public, would their behavior shift for the better?
Aren't you overreacting? There are many possibilities why Wikileaks needs the money.
For one it might be that they had to pay the informant to get the information. Also they probably don't get their infrastructure (including legal) for free.
Last but not least I have to ask you this: Do you equally question every medium that charges for its services? I mean sure, the New York Times and Washington Post uses a different business model, but they charge nonetheless.
Edit: I also have to say that I doubt, Wikileaks wouldn't leak the data in any case.
By the way, TPP is circulating within many governments. For example it could have been leaked by a Vietnamese government official.