Isn't Clint Eastwood right of center? Why would he write a movie to forward a leftist agenda?
I don't think this movie is promoting a liberal agenda. Most of the themes in this movie promote conservative values. It has a distinct pro-freedom/anti-socialist slant, though it is not in-your-face or preachy about it.
Some posters believe it is anti-christian. I did not get that impression. Frankie goes to church almost daily. He seeks redemption through his religion. Frankie is cantankerous and his priest is often exasperated with him, but their relationship was much deeper than than I first thought. It is always the priest that Frankie turns to for advice, though he doesn't always follow that advice. We all fall short of the Glory of the Lord, and so does Frankie, but Frankie tries harder than any character I've seen in a Hollywood movie.
The movie does not advocate euthanizing anyone who is weak or handicapped against their will. It does not advocate euthanizing someone because their family wants it. The issue it deals with is whether someone trying to die should have to fight against everyone else to do it- whether it's ok to help someone trying to die- especially dealing with the grief and moral struggle of making that determination. Characters struggle morally and emotionally with this question, but the movie does not say whether it is right or wrong; to me it seems to leave it up to the audience.