Sort-of memes that are cracking you up at the moment

what if the people who have experienced racism don’t agree/have a range of views on whether they find something racist?

but simply by the very nature of what I am, I can only know less than someone who has actually experienced racism.

This is an interesting point. I think that someone who has experienced racism is obviously best placed to say what does and doesn't offend them in terms of what they find racist toward themselves. For example if someone who is black says said chimp picture is racist, who are we to argue.
However someone from the far east who may often experience racism would be as unaffected directly by that image as any of us and could also too only empathise (granted more easily). So yes of course people who have experienced racism are going to have varied views, they're not all the same.

I think we have a right to offend, it comes with free speech and the rest of it but there is obviously a line, where the line is, I couldn't say. But as you say, if someone finds something racist towards themselves, nobody is better placed to say if they're right or wrong than them and we shouldn't defend it because of "good intentions". Nor necessarily crucify the guy if it was truly a silly oversight though, he recognised the way it looked, removed it, apologised. What more is there?