Do you boycott other industries where companies put competitors out of business? Like Ford, GM and Chrysler? You don't see any Tuckers, DeSotos or Nashes on the road anymore, for example.
I don't shop at Walmart for this and many other reasons ... As far as beer goes, I don't drink beers from MMC because I don't like them, but I do try new "products" when they come out to see if they are getting better (to name one, American Ale is horrible). I try to keep my homebrew inventory well stocked with a bit of variety, so I can always drink something different that I like. When I do buy beer, I am looking for something I haven't tried, really liked, or the style lline of something I'm planning on brewing. I have probably bought as least one of 80%+ of the beers available to me locally. I am a steady but transient beer drinker with no real consistent "goto" beer except Corona (12 pack boxes in the back of the shelf without the finger holes) or Tecate when I'm bored or camping.
With that, I wouldn't consider myself a beer snob, but my BMC friends do.