I understand your point, but I also have problems with colour-blind casting. It acts as though the experiences of ethnic minorities are exactly the same as those of white westerners, but that isn't true today, and was still less true in 16th-century Venice. I understand that it is an ideal that one day casting really can be colour-blind, at least in drama set in the present day, because skin colour genuinely is no longer an issue. But at the moment, casting characters as black without acknowledging that that makes a fundamental difference to how they experience the world around them, and especially how white characters are likely to perceive and treat them, seems to me to be in itself dismissive of non-white people's experiences.