I have nothing against them as a company. I even took a tour of one of their breweries and was quite impressed. But the beer is just no good. I can't fathom how they can screw that up.
It isn't good beer for your taste (or mine either). However, read up on the history of brewing in the US, and you'll understand how they're beer evolved into what it is today (along with the other major breweries, as well as America's taste preference for it). It makes complete sense given the conditions at the time (i.e. very little barley was available, but there was plenty of corn). Their beer is good for what they are trying to achieve, and their ability to reliably produce it in the volumes they do is quite impressive.