That's fair. I think all advertising is naturally bad for the world, but you're right that it's the combination of advertising and greed that created the extremely deleterious environment we have now.
That said, greed fed by other monetization models would not have produced the attention economy, and I don't think the evils of other models (dark patterns for subscriptions, planned obselescence, etc) could have come close to the society-wide damage that the attention economy has caused.
When someone operated a forum in the days of yore, they had the opportunity to put up ads and many did. The difference I think is that they were doing so to fund or offset the costs of operating the forum, not as a profit engine above and beyond the cost of keeping the lights on.