It’s not the flower that is bad. It’s the greenery of the plant that sprawls out and sucks up nutrients and space that the grass needs. If left unchecked they can make a patchy grass yard in a few seasons.It’s really stupid that we care about dandelions at all IMO. Only humans would be dumb enough to drown their own yards in chemicals to get rid of a yellow flowering plant.
Also… they are super easy to get rid of unlike some other weeds, so the ratio of effort to results is high.