By and large, I think agriculture should operate like most other businesses (i.e. be subjected to the free market). However... I think it makes sense to have a certain amount of state influence as well. Simply because, agriculture is what produces most of our food these days, and it's a lot worse if tons of your farmers go belly-up and and you have insufficient food than if a bunch of your automakers go belly-up and ask for a bail-out.
Put in another way, suppose we get rid of agricultural subsidies and then there are 3 really bad years in a row for, say, carrots. A lot of carrot farmers would go belly-up, and either switch to something else, or quit being farmers entirely. The weather might be great for carrot production next year, but if we've already lost 25% of our carrot farmers, we're still going to have a shortage. Across a wider scale, we could potentially have a rather severe loss of farmers in general, and I'd rather somewhat subsidize agriculture than wind up short on food. 100 Euros per person per year, in the big picture, is fairly cheap as insurance for a stable food supply, considering how important food is.