Banksy apparently runs a licensing program. Their artwork is most definitely under copyright, and they rely on trademark protection as well. There is also the

Banksy apparently runs a licensing program. Their artwork is most definitely under copyright, and they rely on trademark protection as well. There is also the practical issue that a lot of content is posted publicly without consent of the copyright owner. It's simply not true that just because someone else committed a copyright violation first, you can commit further violations without impunity based on that first violation.