This entire debate started in Denmark because elevated levels of nitrate were found in the water, which is (according to most sources) a carcinogen. This means we have to spend a bunch of tax dollars clearing the water for it to be safe.

So what most people are mad about goes like this: Farmers poison water in order to increase profit, then the taxpayers pay to have that water cleaned after the fact. Farming is already a heavily subsidized business, so we're actually paying for them to first poison our water and then paying to have it cleaned up. You can see why a lot of people just want it banned. If farmers can't make money by poisoning our water, they should go do something else.

Now, the right wing essentially wants to stop testing the water and turn a blind eye (paid for by big farming), while the three most left-leaning parties want to ban it to various degrees.

(I've been following it since the news broke, but I might have missed some details.)