People leak things to the WSJ all the time. You may not like their Editorial page, but their business reporting is pretty solid and well-respected.
How could providing better protection for their sources be a bad thing?
Why would you assume they would actually provide better protection? Because they said so?
But, then a valid question is "How do we know if Wikileaks provides good enough protection?" and the answer is that we don't know exactly, but we trust it more because of its past willingness to go against the grain and not play along with the govt and corporate entities. Its members are routinely harassed, its head is on some show trial waiting deportation, one of the sources has been locked in isolation for months and months.
I personally wouldn't trust WSF to provide any protection for any important information. I would just assume it would log all the identifying information and when their liason from FBI calls they would be more than happy to provide that info without a court order. That is just my personal attitude towards WSJ.
If you don't trust the WSJ then you are not going to leak them documents with or without this service, right? I mean, it's a tautology: if you don't trust them... then you don't trust them. But trying to make things safer for people who do want to leak to them is good.
As a potential source, wouldn't this make one less confident in wikileaks' ability to protect their sources? I realize that in this particular case it's abundantly clear that he was fingered by someone outside of wikileaks, but it is not beyond the realm of the possible that a flaw in wikileaks' system could leave sources vulnerable.
No because in this particular case, Manning has bragged and got himself caught. It wasn't Wikileaks. But I believe he is persecuted and held in isolation in order to pressure him to implicate Wikileaks. Because of this, one would trust Wikileaks as they clearly do not have a buddy-buddy relationship with the US govt. I wouldn't be able to say the same thing about WSJ.