Some movie roles DO require you to actually be and/or have the appearance of the thing you're playing, why do you think Christian Bale's casting as Moses got so much backlash? Saying it's okay for a 6'4" black man with 6 packs to play a short Asian school girl because non-doctors play doctors all the time, for example is a HUGE stretch.
I can definitely see the other side of the argument, the problem lies when the same people crying foul about this call anyone who has a problem with Green Ranger being girlwashed into Tomi for the hypothetical Power Rangers sequel that won't be coming now a sexist/misogynist (there were definitely some feminists saying that). I don't want Tommy the Green Ranger being turned into Tomi the Green Ranger or Ellen Ripley being turned into Allen Ripley.
race and height are social constructs