Yes, it is OK. It's my computer, and I can run whatever code I want to on it. If I want to run an ad-blocker, that's my business.
If the store doesn't want to give merchandise away for free, then they should stop doing that. When I make an HTTP request, it's just that: a request. Their server can either respond with the page, or not (or a different page). It's my business what I do with the code that the server sends me.
>When a business has high prices or a poor experience, it's customary to shop elsewhere, not to raid the store.
Poor analogy. These websites aren't actually selling you stuff, they're giving away stuff for free, and hoping you'll look at the ads.
If I go into a store that's handing out free samples along with a stack of paper advertisements to look at, and I take some samples and decline to take the ads (or I promptly drop the ads into the trash can), that's the store's problem, not mine. I have no obligation to look at their ads. It's the business's responsibility to come up with a workable business model.