But just because something hurts a business doesn't make it wrong, either. And it's worth considering that businesses are amoral entities - given the chance, most of them will gladly screw you if it increases their revenue.
With that in mind, why should a rational human choose to apply morality to an entity that has no obligation to do the same in return?
(This is not a value judgement on WSJ in particular, more a general statement as to the way of the world)
The way I see it, there are two arguments for this plugin to not exist:
1) "What if everyone does it? If everyone does it, WSJ makes no money and goes away". The appeal to utility. Problem is, it carries the unstated and unsubstantiated assumption that enough people will use this plugin to actually impact their profits in a measurable way.
Because of that, I call this argument invalid.
2) "It goes against the wishes of the content providers". The appeal to morality - but as mentioned above, this is strictly a one way consideration, and it's subjective for each person. There's also the moral consideration that WSJ has chosen to make this content visible for Google users, but only because Google forbids showing different content to the spider and to the human. Then, you're left answering an objectively unanswerable question - is a person who googles for most of their news and ends up on the WSJ often doing something wrong? Or does it only apply when you install the plugin and circumvent the company's intent?
The net effect on WSJ's profit is the same either way.