I've never felt guilty about adblocking
While advertisers continue to allow malware through and to produce large, flashing and audible ads, then I regard adblockers as much of a necessity as having a firewall. When advertisers place nice, I'll consider not using an adblocker, but hell will likely freeze over first. Some sites block me from viewing their content; that is their right. It is also my right to leave their site and go elsewhere.