Number one, you immediately alienate HALF of your audience. Number two, unless you TRULY practice what you preach, in all ways, you will be seen as a hipocrite. There is also the ever-present possibility that you will be revealed as a fool, as well.
Much better, therefore, to keep it to yourself, at least for professional reasons. I have to believe that these stars' handlers tell them these things, but the stars, predictably, ignore them, so swollen are their egos.
It is my understanding that back in the days of the old studio system, the studio honchos like Louis B Mayer and Jack Warner had the "keep your mouth shut" policy as a rule for their performers. They understood show business and how IMAGE works. They'd also NEVER risk a boycott. Every dollar counted.
Ever since Julia Roberts said that Republicans are in the dictionary between reptile and repugnant, I have decided to boycott her movies, and anyone else that wants to insult those of us on the right side of politics.
It's beyond me how many Republicans continue to patronize these idiots at the box office.