A good government needs a strong opposition, so Corbyn has to be good for the good of the entire country.
From what I've seen so far, he seems to be a bit too content in asking what everyone else wants, rather than what he wants. That kind of weak leadership, however well intentioned it is, simply won't pass muster with the British public. People are going to look back on the ConDem government in a few years and think to themselves, "Hey, that wasn't so bad and they did a pretty good job". I'm right leaning by nature, but I agree 100% with Doc that 100% Tory for too long isn't a good thing.