I did not have the heart to break this up. Probably because gnats only live for a maximum of four months, and we are on top of a bar... Fortunately for their romantic objective, they like moist soil medium and we have a lot of that. The adults have no interest in eating the plants but if their is huge larvae outbreak in the soil (unlikely) the baby roots might be at risk.
For some very specific info on gnats, and a bunch of other info on natural insect control in your garden, go here. Go here to see what it looks like when countless thousands of gnats mate in mid-air. Check out the dragonflies and their mathematical hunting moves that one commenter called, "quartering the yard." On top of their obvious size and speed advantage over the gnats, dragonflies can independently move each of their four wings and fly backwards. They also mate in mid-air. The gnats never had a chance, even if they weren't completely distracted.
When I searched Dragonfly sex on youtube the results were way less weird than I thought they'd be, and this amazing video (with a homemade soundtrack?) leads you sideways into an amazing, super technical series of science links. Check out, "Solar Death Ray Water," to see why you should never build a flat roofed structure out of clear vinyl in any place you don't want to burn to the ground.
The plant behind the scene is Lovage number 2. Crow for scale.