Okay, Mario. The movie in question is called "The Intruder" (1961) and starred Shatner as the character "Adam Cramer", a bigoted racist.

Here is the description and review:

Shatner delivers his best performance (actually winning a best actor award at an independent film festival) as a political agitator from "The Patrick Henry Society" (a la The John Birch Society) who incites mob violence in a Southern town to prevent integration. He's a racist, rabble-rousing, skirt-chasing bastard in this one, and Shatner plays it to the hilt. Roger Corman's only serious "message" movie and also the only movie that Corman admits lost money for him. Very good performances by the supporting cast.

Real townspeople were used as extras for crowd scenes, but when they discovered the film was pro integration, they nearly lynched Shatner and company, who had to make the rest of the movie in secret and often on the run. This eventually ended up being filmed in three or four small towns.

So. There you have it. In 1961 Bill was fighting the good fight for integration and risking his health by so doing. What were you doing in '61? I think you scoffers owe William Shatner an big apology, that's what I think. So there!