I am inclined to agree because the deficit will be reduced as a positive side-effect of the growth, while the reverse is not necessarily true. That this, growth will not automatically resume as a side-effect of deficit reduction.
I think there are both ideological and practical differences between the two main parties here: ideological in that Labour favour higher spending while the Tories generally prefer lower public spending. That's obvious.
The second, practical, point is perhaps a little naivety on the Tories' behalf, while a deficit like that is no good thing, it's relative importance in all matters is debatable. I think they've focused on it too quickly, rather than looking at other aspects of the wider fiscal and monetary picture which show the proper way out of, what I like to call in my semi-pro economic speak The Great Fuck Up.
We have to grow our way out of this mess, but we can't afford to have the sort of unemployment and social degradation that the 80s saw, and so that needs to be taken into account when considering where to go from here.
Hence, as much investment as possible. Although a note of caution there