I.... Kind of see what they're getting at. And it's not that their argument is without merit, it's just.... That argument makes you seem like a racist asshole.
Ignoring the hate crime context of it all, the image depicts someone who has been executed, at it's basic level.
The idea of having someone walk around with a depiction of an execution on their apparel... I kind of get.
However, given the context of the image, being who has been executed, it's hard to make the argument that walking around showing the execution of a person depicted as one of the most notorious hate groups ever, is bad because it's a depiction of an execution, without also implying that you don't want kkk members to be hanged, and you're therefore sympathetic to them.
That's a whole "yikes" from me. I certainly wouldn't stop anyone from wearing this, and hell, if someone links it, I may just buy one myself and wear that around. My "yikes" is for anyone wanting to walk the line that they somehow are not sympathetic to the kkk, while still taking issue with this shirt.