Very few people who are alive have experienced the brunt of real monopoly power.
AB Inbev is not a monopoly because the retail market is defined as alcoholic beverages. If you don't like the selection or price of beer, then you can drink wine, whiskey and other spirits that are too numerous to list, hard apple cider, or any number of cordials and liqueurs. AB Inbev has almost zero percent market share and influence on distribution of those alcoholic beverages. In addition, you can also drink water, juice, pop, etc. Furthermore, the necessity of the product is also considered. Alcohol is not a necessity. Then you've got all the market-based factors, such as whether market share is increasing (no, AB Inbev's share is eroding), whether the market participant is able to use the market power to increase prices (no, beer prices are near historical lows when you account for CPI) or force out competitors (no, competitors are increasing), and whether there are any barriers to entry of competition (no, because brewery licenses are freely handed out if you fill out the paperwork and fulfill the reasonable requirements properly, and the only other barrier to entry is a modest amount of monetary capital).
Incidentally, the last time the DOJ tried to break up a monopoly, it blew up in their face (Microsoft) because they had no idea what they were doing.
Furthermore, the comments demonstrate a lack of understanding of how monopolies are controlled nowadays -- by prior approval. Any significant merger candidates need the advance approval of the US FTC and the EU. The monopoly arguments and decisions are made in advance because we know it's next to impossible to break up monopolies once they are formed by combination.
BTW, it amazes me what a bunch of whining babies home brewers can be. If you don't like NB, then go shop somewhere else. That's why it's a free market. Besides any LHBS near you, you've got the choice of at least a dozen reputable and high-volume online retailers who will ship to your door. (NB, MS, HBS, B3, AIH, Ritebrew, L2B, Rebel, Bell's, AHS, Label Peelers, Wine and Hop, the list goes on and on ...)