I am really getting fed up with this crap. Dame Helen is one of the classiest, talented and most beautiful actresses of the last several generations. She can play whatever she wants.
If we flip this, Jewish actors and actresses (including Scarlett Johansson, Harrison Ford, Natalie Portman, Sean Penn, among many many others) should not be allowed to play other than Jewish roles. Jake Gyllenhaal would certainly not be able to play a gay cowboy. That is absurd. On the other hand, there is a movement to have Black actors play roles that have traditionally been considered White characters. A Black Spiderman? Why not?
This trend seemed to begin, in my recollection, around White actors playing the roles of indigenous Americans. That was an important step, but it was primarily because indigenous American actors were available but not being employed in roles that were perfect for them. Then the trend flipped to stop limiting certain ethnic groups to stereotypical roles (Mexican drug lords, Black gang members, Middle Eastern terrorists). All of that had its place and were important changes.
The identity social movement has its values, but has gone waaaaaay overboard. We are a culture of moles thinking our little holes are mountains. The more we separate into our ethnic/gender/sexuality bubbles the harder it becomes to unite for good causes. This damages our chances to make meaningful progressive changes in the world.