1) Spam is not the same, you didnt ask for it so you are rightly refusing and actively blocking it.
2) Content is not free. Someone had to create it, and they can either charge you directly or let you see it for free by also showing you ads. When you block those ads but still read the content, you're stealing the access/time/production/value of that content without letting the publisher recoup any of their investment or make any profit.
3) I'm not really sure where this anger comes from. Advertising is such a big and growing industry because it works. This is not some evil conspiracy nor are all the companies full of idiots. You will find regular people much like yourself working at all of the advertising agencies, networks and publishers.
Impressions do work. It's not a "belief", it's a fact. Think of it like an empty road with a billboard and a store at the next exit. You can have a blank billboard and see how many people stop at the store. Then put up an ad and measure again. That delta is a significant and measurable difference and with digital advertising, it can be tracked to a very specific level to prove it works. There are also many different types and formats of ads which work in different stages of the sales conversion funnel. YOU might not think it works, but that's not what the massive amount of data and results show every day.