When it comes to monetary exchange, we are either artists or consumers. AI art has the potential to create a massive imbalance between these two fields, reducing the friction of being a consumer, and greatly reducing the number of people who are able to support themselves as artists. If you view yourself chiefly as a consumer this might (very narrowly) be viewed as a positive.
The social cost however is creating a society that favors consumption over creation, and weights incentives accordingly