There are two forms of bad art: something that is ugly, and something that is done by someone without actual skill. The latter is arguably worst because it manifests in aesthetically unpleasing work, the use of trite or facile themes, etc: essentially, a faux artist summoning amateurish ideas.

How can bad artists exist? Because the ego exists. So a big ego in an artist with poor vision, poor execution and delusion that he is an artist is a recipe for bad art.

Someone who could not do the basics such as drawing, color mixing, understanding and applying values of light and dark, would not call themselves an artist because their end product would not be good and they know it. Abstract art can be stated as good by its creator and justified by the ‘all art is art’, or ‘beauty is in the eye of the beholder’ arguments and bypassing actual skill and artistic capability.

Rothko, Pollock, Picasso, to name only painters–everyone who deviated from the traditional all had a firm understanding and ability in what they were breaking away from.

You ask how do you distinguish good and bad art in the abstract world? The simplest answer is by the artist.

So I will say this: not all abstract is bad art, but all bad artists are abstract artists.