Are we allowed to pretend that without adblocking, the Web is pretty much unuseable?
Define unuseable (for instance: how fast a page needs to load, how good the layout should be, how little bandwidth should be used). I'm sure there are plenty of sites that fit to whatever reasonable definition you provide.
You don't have to like the entire Web, it's not yours. People provide services and either you like them or not. If you don't like them, then don't use them (boycott).
There are plenty of parts of the web that are usable even with ad blocking. People complain that the web was "better in the old days", but there is nothing to prevent those folks from going to ad-free sites and offering their own sites without ads (or with "friendly" ads, whatever that means) too. The Web is not a single monolithic thing, but many different services and communities.
As I was suggesting above, make a proper "boycott" plugin and only go to sites that you like. You can even customize what you like (whether it has commenting, tracking, advertising, bad content, a newsletter popup, too slow, bad layout, bad editorial policy, bad content, or whatever reputation rules float your boat). If you find parts of the web un-usable, then don't use them.
Do you think that the cost of visiting the sites with ads should include slowing down page loads and getting infected with malware?
That means you should avoid them, just like you avoid restaurants that don't offer a worthwhile trade-off in your view. Boycott is a perfectly valid choice and I encourage it.
Just don't pretend that getting the benefits while dodging the costs is "boycott", when it is free-riding.
Science and religion are in full accord but science and faith are in complete discord.