I can stretch as far as saying that if a blocker can detect it, it's too invasive. That includes, for example if it is served from an ad network.

I don't mind ad pictures in magazines. The same should be ok on websites.

Im not sure what fraction of the Internet is paid for by ad-network revenue, but I really don't care if half the content on the Internet suddenly dies in a fire because their measly income from ad networks dries up. I'm happy with only truly free, properly monetized (affiliate links, proper sponsoring), or paid for content.