Charlton Heston's political descent into right-wing crankery never really made me think less of his films--at least his better ones--just as Alec Baldwin's liberal activism doesn't make me think more highly of his. (Or, for that matter, make me value Heston's films of the 50s and 60s, when he was himself a Hollywood liberal, more than those he made during and after his political conversion.) Whether actors choose to exploit their celebrity status in order to promote favored political causes is ultimately of little interest to me, although I certainly reserve the right to find their political views obnoxious, as I often did find Heston's.
Unfortunately, Heston was for the most part a rather wooden actor, so it's only in a handful of cases that one has to make the effort to separate the work from the man to begin with. Most of Heston's bad films (and there are many) fail because of poor scripts and/or his own undistinguished performances. Moreover, in some of his better films their success comes at least as much from the compensatory skills of the director (Orson Welles, Anthony Mann, Sam Peckinpah) or from a fortuitous match between role and Heston's impassivity as an actor (the various spectacles with which he is most closely identified). One remembers that Heston was in these films, but it is not his skills as an actor that make them memorable.
A significant exception to this pattern is Will Penny (1969), a relatively overlooked Western that depends entirey on Heston's sensitive portrayal of the eponymous protagonist, an aging cowboy who suddenly finds himself forming a family with a stranded married woman trying to make her way to California along with her young son. While Heston's previous "strong, silent" characers were laconically heroic, larger-than-life figures, Will Penny, though equally laconic and with his own kind of inner strength, is a modest, in some ways nondescript man mostly concerned just with surviving from season to season. Heston manages to find both the strength and the vulnerability in this man, and although the film creates considerable emotional resonance, it does not sentimentalize Will Penny and his circumstances, primarily because Heston manages to make the character's guilelessness, his essential innocence, seem genuine.
Will Penny probably belongs among the other "revisionist" Westerns of the late 60s/early 70s (The Wild Bunch, Little Big Man, Ulzana's Raid), in which the conventionally heroic view of the American West, complete with gunslingers and persevering ranchers, was subjected to vigorous critique. In this case, the West is depicted as a place of hardship for those trying to extract a living from the land, the landscape itself rather bleak and blighted, including by those inhabiting the landscape, such as Quint (played by Donald Pleasance), a lunatic preacher who with his depraved sons stalk Will Penny almost to his death. Will Penny himself seems a revisionist Western hero, an unassuming, instinctively nonviolent character who even when he rides off into the sunset at the end of the film does so less as a gesture of rugged individualism than as a consequence of his own self-understanding--as much as he loves both the woman (played by Joan Hackett) and her son, as much as a settled life might appeal to him, he knows that he is too old and too habituated to his cowboying existence to adapt and that the woman, Catherine, should not be asked to sacrifice her marriage for a life as difficult as that she would share with him.
Heston manages to convey Will Penny's struggle to resolve his own conflicting impulses--to live an ordinary family life and to be honest with himself and the woman he loves--with affecting authenticity. Indeed, his performance is probably all the more convincing because of our association of Charlton Heston with Hollywood-style heroes of great determination if little depth. Will Penny seems to allow Heston to express facets of his talent his other roles forced him to suppress. In the process, Heston's performance in Will Penny helps to de-mythologize both the Western hero in particular and the Hollywood image of masculinity more generally. I don't know for sure what the later NRA President would have thought of this, but his opinion isn't really important, anyway.