It was definitely Alda. IIRC, he became a producer midway through the series and was pushing his lib agenda to be integrated to the plots.
They're still damn entertaining, no matter the subtle politics thrown in during the latter seasons.
That, IMHO, was part of the greatness. Yes, there were politics, but they were subtle, and much more "here, think about this" compared to modern "think this way or else". I'm still short the last couple of seasons on DVD, so I may be remembering wrong, but that's how it seemed to me.
Always liked that show too.
KC
One of the OTA channels that has spouted up is Grit, it plays tons of western TV shows and movies. See lots of it when we visit my father in law. 99.9% The Rifleman is on regular rotation there.