Actually, there is no reason not to like 'em. They are a dual mixture of organisms - a fungus and a colony of green algae. The most popular that people are familiar with is the blue-green algae also called cyanobacteria.
The algae and fungus living well together and getting from each other what they need makes for a nice relationship called symbiosis. Lichens will occur in a very wide range of habitats - anywhere from the deserts to the arctic. In the arctic, reindeer and caribou depend on lichen for their primary food source.
Because lichens can withstand extreme and varied temperatures they can exist on mountain tops.
Lichens will also range widely in color from the grays, black, white, blue-green, to bright red and orange, and brown. The color often is developed because of water content.
Lichens grow extremely slow - anywhere from 1/25 to 1/2 inch per year and have long lives.
Other than being considered unsightly by some, lichens rarely do any damage to plants.
When these ideal conditions for algae and fungus occur, perhaps the conditions should be improved or changed to eliminate or diminish their growth.