When making international comparisons between countries, there will never be a perfect correlation because unlike in a physical experiment, you can't control every other factor, but nonetheless, there is still a strong correlation between austerity and (lack of) growth.
Nothing is guaranteed in life, but don't you think we are betting against the odds with austerity, given recent economic results (unemployment in the UK has worsened under this government) and the evidence presented above, and despite countries like Ireland and Portugal continuing with their austerity plans, the results aren't getting better. What a lot of people don't comprehend is that when these policies fail, people pay with their livelihoods - the 50% or so of youths unemployed in Spain will never get those years back.
As for the 'motives',The first graph is from a Berkeley paper, I believe the 2nd graph down was published for an economics paper on fiscal policy, the last one was down by Oxford Economics and Fitch, who are pretty reputable.
I have now actually found the graph I wanted, and it is based on IMF data, and shows the countries of the eurozone, and is similar to the second graph, but over a longer period - and it is consistent with the findings from the other data: