The argument for paying down our debt is usually to prevent inflation or keep future borrowing cheap, but despite the plunge in GDP neither of these are anywhere close to becoming an issue.
Speaking of GDP - it's not the deficit that's responsible for the US's decreasing GDP/debt ratio, it's the drop in tax income due to the job losses following the financial meltdown.
There is plenty to dislike about how the stimulus turned out (too small, partially negated by state-level cuts, focus on tax cuts), but no evidence whatsoever that it made things worse.