In many forums, it seems more like a racism debate. It's not PC to complain about a "black" actor taking a role that may traditionally have been filled by "white" actors, but there is a fierce anger about casting a "white" actor (man, I hate this discussion) in a role that was traditionally held by someone of colour (and I don't include Spanish RM here). Perhaps the intention of the posters is noble, they presume they are defending the rights of black actors. But it's all just racism to me.
I just assumed this was colour-blind casting (a practice perhaps more common in Britain than the US) and that the job went to the most impressive candidate. There may even have been some sensitivity around pushing the idea of sub-continental terrorists at this time in our history. But after that, I didn't think any more about it. The vehemence of the debate has shocked me. Maybe I'm missing something.