But by that logic, Alisa and 24 should have only hired actors who had previous experience working as spies, counter-terrorist agents, and actual terrorists, Prison Break and Orange is the New Black should have only hired actors who had served actual time in Prison, and Mad Men should have only hired actors who had worked for advertising agencies in New York during the 1960s.
Some actors do research and invest themselves in their roles and we do see the results pay off (see the many actors who play alcoholics and drug addicts). In the Meryl Streep example listed above, it sucks that she had to do all of that work when there should have been more people behind the camera helping her out and supporting her, and also taking a more balanced look at the issue. Not saying she should have had to do it all herself, it definitely should have been more of a collaborative effort from all involved.
The same for Eddie Redmayne in The Danish Girl; him learning about what it is to be a transgendered woman is just one other acting hurdle, and it isn't like that is the only acting hurdle to deal with. If there is enough support from the writers, directors, producers, etc - if they have done the correct research as well - then there shouldn't be any problems with the nuance of their performance.
Which for me, goes back to the issue of non-American non-white actors playing roles of the same ethnicity but as Americans (or the other way around). If they and the people behind the camera put in the right amount of effort into researching the role and what is required for the role, then I'm ok with it.