In our court system, there is a legal principle of 'Ignorantia juris non excusat,' or essentially, you cannot use the "I didn't know I was committing a crime" defense in a court of law to excuse yourself of culpability.
As an artist (and as a person), I firmly believe it is your duty to understand the full impact of the statement you're putting out into the world. In a day and age where we can access images and information readily, it's just not really an excuse to say that you didn't know blackface (or casual rape references, or homophobia/transphobia, or misogyny) were problematic. If that's really true, I would urge you to take an honest look at the world you're participating in, the people you're surrounding yourself with, and the type of information you're accessing.
And I also feel like if you feel that you need such a two-dimensional, unoriginal, and uncreative devices to make your artistic statement, then I question if you're really making art. If you can't stand up and defend your artistic choices and explain what original thoughts you were trying to present, then what are you doing? And most importantly of all, if despite your thought, care and effort, if a large portion of your peers are telling you that you are creating art that is actively hurting a large community, are you really willing to stand behind your act? Controversial or boundary-pushing art is one thing; using a cheap device as an attempted "shortcut" of sorts to connect with your audience (or worse, rely on "shock-value" to pass as art or entertainment) is more often the reality.
Blackface is the willful appropriation and propagation of racist and hateful stereotypes. It is exploitation. It has a long, long history of trying to systematically devalue the black community and trivialize their experience and trying to pass it off as art or entertainment when it is really a stupid parody at best and a dehumanizing weapon at worst. I feel this way as a white person that is incredibly horrified and humiliated by this part of American and British history; I can't even begin to fathom the sort of complex emotions someone in the black community must feel when watching blackface still being practiced today and being glibly passed off as entertainment.
I don't think tar and feathering is the answer, or ripping these people to shreds through public humiliation. I think being honest in your pain and experiences is completely justified and expressing that to these people who commit these offenses is necessary.
I have reached out to the artists pictured, especially after I read the act's description:
"It's a double act - Enter a woman in a tropic helmet. She is obviously hot and sweaty. Enter the black-faced protagonist, who shoots a poisoned dart, then drags the sedated explorer and puts it in her giant cauldron. They squabble and take each others bras off. When they resurface, they are no longer fighting but have fallen in love."
There's a quote I like by Jean-Luc Godard: "It's not where you take it from, it's where you take it to." However, I suggest the edit "it's not only where you take it from, but where you take it to."
In this case, I urge you to research where you're taking these devices from - the history of minstrel shows and blackface - and I ask you, where are you taking this dialogue to? What original thought and ideas are you trying to present? What makes this art? Are you willing to stand behind this?