You don't need to trust 'em. Worst case scenario is that you leak to 'em and they ignore it so you go take your leak somewhere else.
Competition is always good. Whether or not wikileaks has obvious "conflict of interest" they have a certain ideological outlook, and having a competitor with a different ideological outlook might help in cases where wikileaks chooses to sweep something under the rug.
You have to trust their promise that their anonymous submission process is actually reasonably anonymous. Many whistleblowers probably couldn't tell between an anonymous process and a seemingly anonymous process that isn't.
Right. But in this case trusting WSJ to keep your anonymous submission secure as well as trusting their ability to run a leaks site would be a mistake:
So how to they catch all those "online pirates"? I am sure they don't provide their address, name, and social security number when they download a song for example. However that has not stopped thousands upon thousands of cases to be filed (now whether you think identifying people by IP is right or wrong is besides that point, it is happening and it is part of the system). So "no" you should not leak anything to these people unless you know every well how to hide (chances are you might not, even your browser's identifying info like fonts, OS version etc. can be used to narrow down the search and there are other things as well).
If you're going to be that paranoid, you should consider carefully the credibility of whoever you're leaking things to. Do they have a track record of keeping secrets? How hard are they for The Man to pressure? And so on. Wikileaks does very well by those criteria. The WSJ has less of a track record, and inspires less confidence with their privacy policy and somewhat dubious web site security.
The best thing that could happen is that the WSJ hears criticisms like this, takes them to heart, and turns into a serious competitor to Wikileaks. As it is, though, they've got a lot of catching up to do.
Competition is always good. Whether or not wikileaks has obvious "conflict of interest" they have a certain ideological outlook, and having a competitor with a different ideological outlook might help in cases where wikileaks chooses to sweep something under the rug.