I live in a poor neighborhood in a reasonably large city.

I shop locally (even avoiding the more affluent neighborhoods), exclusively if possible, as a matter of voting with my wallet because the businesses in my neighborhood employ mostly local folks.

At large scale, yeah, you're right. But for a small local business, one or two extra regular customers can be a bigger difference (drop in a bucket vs drop in the ocean). Even something like shopping at a local big-box supports the local proletariat more than shopping at Amazon, where the proletariat isn't guaranteed to be local at all (and to be clear: it's more about supporting the proletariat than the capitalists).