The economy does not grow when the state borrows and spends money. The economy grows when private enterprise creates products and services. For private enterprise to flourish we need low taxes.
And yes, we would know what would happen in 2010 with debt if Labour won election — because we know what their budget was. And the numbers in their budget meant that the debt would grow more in 2010 then it grew in 2009. The new Conservative/LibDem budget ensured that the grows of debt slowed down.