Reductio ad absurdam
If it's unethical to block ads, is it also unethical to fail to respond to them ? Presumably clickthrough gets the publisher more revenue than simply viewing. Maybe referral gets them more still.
If anything from failing to purchase the object, to failing to clickthrough, to failing to move your eyes to that point on the screen, to blocking the ad completely denies the publisher revenue, then are those all unethical too ?
If not, where do you draw the line ?