I understand what you are saying. Trump's behavior transcends politics and is an affront to basic human dignity and it must be challeged at every turn and in every forum available. Where I disagree is that I think that Streep's comments were about politics as well because like it or not, Trump is now a politician. He is an inept, inexperienced, ill tempered, politician without ethics; but he was elected to office and entered willingly into politics. He will be in charge of executing the laws and policies of the country come January 20th.
People tend to try to separate politics from everyday life, but politics helps to shape everyday life. The policies that are made and enacted affect us and the people who are placed into positions of power shape those policies. Politics has two meanings, one is a narrow focus that deals with the workings of parties and the organization of states. The second, broader one is what is important: politics has to do with the affairs of citizens. What does it mean to be a citizen, what responsibilities do citizens have to their fellow citizen and to the state. What responsibility does the state have to citizens, residents, and people trying to find a better life. Trump, his followers, and the Republican party in general are trying to redefine America by closing it off to certain people. They are trying to, in some ways, take the country back to a time where there was less influence by the national government, where the social order established by wealthy White Christian Males was not able to be challenged so loudly as it is today. Trump's own behavior is the product of an upbringing where money, the right race, and the right gender were deemed enough to obtain anything or excuse anything. He and his ilk are injecting that into society. That is politics.
To the question about celebrities... The only acceptable answer in my opinion is also YES. They have every right, as any citizen, resident, etc... has to comment on what they see. Hopefully, with their resources, they take the time to study and provide informed and intelligent discussion about those serious issues, whether they coincide with my own opinions or not.