I'm black and I honestly don't think it's racist at all because I completely agree with it. Certain comic book characters are so iconic, you really should portray them the way they've always been. I have no doubt this is done by the production just to score some P.R point on some level.
For me I wouldn't understand why the move has been made, personally I don't see the need for a black Kal-el (just have another black Kryptonian arrive and bingo). It wouldn't stop me from seeing the movie tho, and it's possible it could be great. I rarely get hung up on the changes made in adaptions.
It's not a big deal to me. I thought Cavill was good tho and really like MoS. So it's a shame...
Someone above said they think Snyder hates and doesn't get superman. I think his Superman has been good. Apart from the whole collateral damage in MoS thing (I understand the criticism but I justified it as untrained Superman trying to do what he can and enjoyed the fireworks), and his demeanor which is more grounded in his current context, he's been fine.
WB need to sort their shit out, they aren't far off righting the ship but they seem more set on making it worse (not saying MBJ would make it worse, it's all the chopping and changing).