There are certain topics and real life issues that matter to the movie fans regarding the actors/actresses they will support. Some topics may not be a big deal, i.e. pirates, medicine, history, etc.
Other topics may be more important than others; 2A rights for example, or freedom of religion, or pro/anti-abortion, etc. because they actually matter to the movie-goer.
In regards to Stallone (or any action/firearms actor) and being anti-gun, he will be seen as a hypocrite along with others who are on the same boat.
If Chuck Norris or Steven Segal were anti- self defense then I would stop supporting them also.