I'm an actor, primarily Shakespearean. I actually get cast in quite a few male roles - I'm tall, with broad shoulders and narrow hips in proportion to my frame, and quite a low voice.
I'm happy about that, as there are so few good female roles, even in Shakespeare, especially for older women (and my build and voice meant I never got the good younger female roles when I was young - I've never played Juliet or Ophelia, for example).
But for the same reason I'm against completely gender-blind casting. Men have so many brilliant roles to chose from, so they can keep their grubby mitts off Gertrude and Lady Macbeth!
I realise this may not seem very equal, but I think it is nonetheless fair - in the same way that I have no problem with black actors playing Lear or Hamlet, but white actors shouldn't play Othello.
Emma Thompson can play any role she likes, IMHO. She's great.