Graffiti and intellectual copyright

Today, I returned home and checked RB as I do almost daily. I found that I’d had several angry comments on about half a dozen images of graffiti taken on a recent urbex.
These comments were from two graffiti artists whose work I’d taken photos of and posted on RB.
They were exclamatory in tone, incredulous that I was apparently “making money from their art.” They were very upset that I had somehow stolen their work and so decided to leave aggressive comments, (now deleted).
I had also previously posted the images on Flickr and today, also received an angry and aggressive message stating that it was “forbidden” to be making money from their art. Despite this being nonsense legally.
After a short back and forth (which you can see at the link above) I decide…