I've observed that some less-savvy people don't know how to unsubscribe from emails, or fear doing so will "upset someone" and so grin and bear an otherwise annoying deluge of email they never react to.
It doesn't feel great to be told you're unimportant, and no company owner will say that to their own customer, but really — you and I are not that important. I do not expect McDonald's to abolish all their meat products because they offend me as a vegetarian — the rest of their customers manifestly do not share that opinion, so it would be a dumb choice if they killed the Big Mac. Similarly, it is not in a company's best interests to terminate an objectively successful email campaign just because some random guy got pissed off but was unwilling to click Unsubscribe. Successful companies lose customers all the time for all kinds of reasons — they would never get anything done if they tried to personally appeal to every single person on earth.
Again, McDonald's pisses off millions of vegetarians every single day. Would you say on that basis that they should go meatless? Should churches close to avoid pissing off militant atheists?
The point is not that you should be callous about offending people. Obviously it is better for all involved to make people happy, and that should always be your goal. But the point is that one or two guys saying "I'm so angry!" on an Internet forum does not mean you've failed. No matter what you do, even if it's pure charity work, you'll eventually find someone who gets upset about it. All you can do is apologize and offer to unsubscribe them — it's not rational to throw your business away on that basis.