Incredible as it may seem, I've actually seen that asserted. Years ago when I was a kid, before we had internet, my family would get a lot of magazines. Whoever picked up the mail, usually whoever came home most recently after it was delivered, would flip through every magazine and tear out all the advertisements and throw them in the trash before putting the magazine on the counter for the family to read. I wonder, was that 'theft'? We also used to change the channel or mute the television/radio whenever advertisements came on. Was that 'theft'?

Usually people who call adblocking theft start squirming when these pre-digital examples of ad avoidance are put to them.