That's not very productive. Anyone on the pro-SOPA side can say exactly the same thing about e.g. Google. One of Google's major divisions, Youtube, was built in part on piracy. And Google itself does help people find pirated content; that's not something immoral, and they do make it difficult, but Google benefits from some copyright infringement in the sense that it means they're a better default search engine, since some fraction of queries are for copyright-violating content.
And the WSJ article does make a similar point:
Wikipedia has never blacked itself out before on any other political issue, nor have websites like Mozilla or the social news aggregator Reddit... They've taken no comparable action against, say, Chinese repression.
This is not the first thing so awful that websites choose to take such action--it's the first awful thing that threatens them so much.
The WSJ also points out that the most egregious part of SOPA--DNS-level censorship--was removed in the latest draft. They don't make an exceptional argument, but they do make a superficially reasonable case; someone unfamiliar with the way the Internet works would likely find it pretty convincing.
SOPA/PIPA is an awful, awful idea. But if the WSJ claims that it's a good idea, and you claim that the WSJ only says so because corrupt, then you lose by default. The WSJ can have a good argument that defends their economic interests, or that is hypocritical in light of what they've been caught doing in the past. SOPA opponents are in a very similar situation.