Do those that are anti AB also avoid Walmart, Target, Amazon, Home Depot, Lowes, Best Buy, Total Wine, Specs, BevMo? All of those can be considered anti competition.
I do my best to avoid those stores, but sometimes there aren't very many choices. If you live in a smaller town it can hard to shop local for things like clothes or hardware. Hardware stores and department stores have just closed in the past decade or so. I also avoid AB-inbev products, although it can be hard to keep up with which breweries have been bought out.
On the other hand, Northern Brewer is an online store - not unlike Amazon. There are a bunch of online homebrew stores that are comparable to NB in selection and price that are independently owned. I'd prefer to use them.
Finally I'll say that I'm not an absolutist. Sometimes I will use a big box store or an online store even though a local store might carry a similar product at a similar price. My plan is just to try to do a little bit better about helping out the people who have an interest in keeping the money that I spend within community that I live.