OP’s talking about the time taken to write the text, not the hosting costs (which would be zero on GH Pages or something like that).
It's an old-fashioned notion, but the advertising industry has extremely bad manners: it doesn't respect civilized social norms like not exploiting personal information for private gain and not egregiously interrupting people for trivial reasons. It's nosey, untrustworthy, intrusive, manipulative, and deceptive. I wouldn't tolerate this behaviour from a friend, and I'm not going to tolerate it from a bunch of amoral strangers.
edit: and it doesn't help you much, you are likening ads to harmful things.