I'm old, so I'll tell you what I remember:
Sixty Minutes did a segment on Coors in about 1980 or so. Coors would not let a union in, so that's probably the grievance you remember. The workers at Coors said on camera that they were happy with how they were treated at work and didn't feel they needed a union. But I remember it being all about union issues.
The Coors family are ultra right wing (not sure about their South Africa connections, but it's possible because Republicans have an abysmal record for how they treat blacks and women), but it is possible you are both a little bit right.
It doesn't take much effort on liberals' part to boycott one brand of beer that tastes pretty much like most of all the other beers out there.
As a funny aside, I used to drink Schlitz beer in college, which was horrible beer, because when Frank Shorter was asked in Runner's World magazine what his favorite snack was, he said he loved "Ding Dongs and Schlitz beer." It made me run faster to the bathroom.