What's wrong with Ants?

One thing I know of, is, they keep lice! as we do cows. Maybe, just some species like to do that. They take the sweet excretions.
One another: they like certain plants, which maybe You don´t. And they collect the seeds of them. (Don´t know, what they do with them).

Actually on the plant they, in themselves, do little damage. They do keep aphids and 'milk' them for the plant sap, even moving the aphids from stem to stem and protecting them from predators.
In the ground their nests under plants can and do kill off the roots, especially under Dianthus.
On the plus side (or maybe minus?) they do collect and accidently sow seeds of various plants. The seeds have a sweet coating which the ants lick off and then discard the seed. Cyclamen are dispersed this way.
Personally I ignore the nests where they are not damaging plants.

Yes, as above, ants do farm aphids, they are their cows. They take them to the top of the plants to the lush tips. When they are very large and full of sap they take them back to their nest squeeze them for the milk for their young and the adults eat the rest. At the same time they will transfer virus to many plants, they are more harm than use. Anything in their path is used in the manufacture of their nests.