I did answer your question. I said the delivery for television is when it is broadcast through the air or cables. Which it is, regardless of if your television is on. Just like how radio waves are in the air whether your radio is on or not. Even if the radio never plays the sound, the data is still being broadcast (aka delivered).
The mail comparison quickly falls apart, since you do not benefit from spam mail. You do not get a service in exchange for getting the spam mail, so what could you steal by not getting spam mail? If you put up a sticker that prevents the delivery (kinda like an ad blocker), then you did not get that ad delivered. But again, you are not using advertising mail as a means to pay for a service you are using, so it cannot be stealing.
YouTube is not free. Period. It costs money. Google has to get money from users to run it. It can either do that from ads, subscriptions, or donations (which we know isn't going to happen). If every user blocks ads, no ads are being delivered, and they would not be able to run the service. In our world, ads are tracked by delivery and not by eyes seen. End users can choose to look away, ignore, walk away, turn off their monitor, or whatever else. The ad was still delivered. Ads delivered means a small percentage will learn about their business through those ads, which makes it profitable for businesses to keep paying for them. Therefore, to block ads, you are not paying for the service. To not pay for a service that you are expected to pay for is stealing.