I don't think it is piracy. Most advertising supported content is made freely available to you with the expectation that you will view the advertising. That expectation is not a contract and was a decision made without your involvement. You have no obligation to perform to someone else's expectations. If the content is made freely available you are free to watch it whichever way you choose. Choosing not to view the advertising might mean they don't get paid for producing their content, but you are under no obligation in the absence of an agreement.
Piracy involves you deciding to acquire content that has not been made freely available.
Piracy involves you deciding to acquire content that has not been made freely available.