I honestly don't think the problem is austerity or keynesianism or whatever. I'm more concerned with the way politicians are handling budget in general, period. France's debt is so ridiculously big, one of the largest areas of spending in France's budget every year is paying back interests. Not paying back the debt, just the interests. Over 41 billion in 2017, 4rth largest area of spending, ahead of defense for example. And it's only going to get worse, as France is operating at a deficit. We keep borrowing, while we have no chance to be able to pay the money back in a reasonable amount of time. The debt is at about 2300B. If we had no interest to pay back, had no deficit, and used what money we're paying this year to pay back capital every year, it would take 2300/42=55 years.
Saving a little money here and there is not gonna solve the debt problem. Not in this century anyways. Spending a little more is not going to make things much worse than they already are. I could see unreasonable spending raising interest rates and making things spiral out of control. But, reality of it is, there needs to be some fundamental change to the way economy is structured if the problem is going to be actually addressed. Fillon's version of austerity for example is not gonna solve the problem. Not saying I have answers. But I'm not seeing any credible ones proposed by the candidates either.
Debt is a natural component of capitalism, it is normally counterbalanced by inflation. No country ever payed his debt.