Government paying people to burn food supplies.
1) you get some small amount of oil out of it.
2) if shit hits the fan, you have local farmers, with all the equipment and knowledge/training, who can immediately switch to food production if needed. The alternative would be to train new farmers, buy new equipment, etc., which would take a long, long time (especially if the government is organizing it), and there's that saying about two missed meals and a revolution, and french leaders really really don't want another revolution.
We all understand that, in an ideal world, most forms of (consumer-focused) insurance are a blackhole that you dump money into and never actually get any money back, because insurance only pays out if things go awry.
Subsidising strategic industries like farming falls under that exact same rubric. Ideally you don't ever want to cash in on that investment, but it's important that it's there. The CHIPS Act in the US is an example of this idea exactly. In a world where China is getting more aggressive around Taiwan, US-based foundries are an (expensive) insurance policy.
The main reasoning is something like this:
Climate change bad, green bio fuels good, subsidize as much as possible. We're subsidizing farmers like crazy anyway so maybe we can turn that fund into align with our other goals a bit. Oh wow we didn't realize there would be side effects.
The point is that countries have to keep their farms in working condition, whatever we make farmers do. And yes, biofuels are a way to achieve that, the alternative would be to farm too much mustard, which is not ideal either.
And yes, as a side effect, a bad harvest in Canada and and a war in Ukraine can cause a temporary shortage of a non-essential food item. It sucks, but worse things happened in the last 2-3 years, including shortages, and it wasn't about farming. And I say that as someone who is directly affected by the mustard shortage.
And there is lot of reason the be snarky about the EU, I mean the fact they keep moving every few months for hundreds of millions of dollars is extremely disrespectful to the European people. Let alone their disregard of national democracies.
4) co2 balance of those 'biofuels' is way worse than fuels refined from extracted fossil fuels
5) additional supply of these fuels lowers fuel prices thereby slowing shift to renewable energy sources (i.e. renewable electricity)
6) simply paying farmers for fallow fields is a much simpler solution to the problem
So, when shit hits the fan, you have farmers who can't increase production, because they don't have the resources, and you get speculative investors who jump ship, plus a lot of empty fields and hungry citizens, revolution, guillotines, etc.
If those areas are now producing crops, you have a guarantee, that the farmer can actually handle those fields, that the equipment is in working order, you know how much they can produce, and all it takes is just to switch the corn for eg. ethanol to corn fit for humans to eat.
By what metric? You get out much more energy than you put in. And when we're talking about keeping farms active, that land wasn't going to be doing something significantly better wrt carbon if the subsidy didn't exist.
3 does not really apply in France. There are extensive swathes of country which are hugely monocultured already with food crops. At the same time small farming, economically uncompetitive types of farming, and other forms of land stewardship are extensively supported by the state in various ways. The question of monoculture is much more complicated than to think that growing rape for biodiesel is going to remove biodiversity.
I think farming is not as fungible as you think.
> which would take a long, long time (especially if the government is organizing it),
The government seems pretty adept at forcing people to learn some basic skills pretty fast and forcing others to make heavy equipment when wars occur.