I don't think "ads make people buy stuff they don't need" is a large part of what's going on. One way to think about this would be, what would the world be like if we didn't allow advertising? Not just internet ads, but magazine ads, affiliate links, sponsored posts, product placement, everything. And assume that enforcement is perfect ;)
Here's my speculation about how this would change people's purchasing:
* Products would be a lot stickier. A lot of advertising is about trying to move people between competitors, or keep them from moving. Sometimes it's an explicit "here's a way we're better" (ex: company advertises that they don't charge unpopular fee X), other times it's a more general "you should think positively of our company" (ex: we agree with you on political issue Y).
* Relatedly, it would be much harder to get many new products started. Say a startup makes a new credit card that keeps your purchase history private: right now a straightforward marketing approach would be (a) show that other credit cards are doing something their target audience doesn't like, (b) build on their sense that this isn't ok, and (c) present the new card as a solution. Without ads they would likely still see uptake among people who were aware of the problem and actively looking for a solution, but mostly people would just stick with the well-known companies.
* Purchases of things people hadn't tried before would decrease, both things that people were in retrospect happy to have bought and things they were not. One of the roles of advertising is to let people know about things that, if they knew about them they would want to buy. But "buy stuff they don't need" isn't a great gloss for this, since after buying the products people often like them a lot.
This is just my guesses; I work on the technical side of ads and don't have a great view into their social role, and even if I was in a role like that it would still be very hard to predict how the world would be different with such a large change. Where does your picture differ from mine?"
(For 'saving the planet' I think a carbon tax would make a lot more sense.)
Here's my speculation about how this would change people's purchasing:
* Products would be a lot stickier. A lot of advertising is about trying to move people between competitors, or keep them from moving. Sometimes it's an explicit "here's a way we're better" (ex: company advertises that they don't charge unpopular fee X), other times it's a more general "you should think positively of our company" (ex: we agree with you on political issue Y).
* Relatedly, it would be much harder to get many new products started. Say a startup makes a new credit card that keeps your purchase history private: right now a straightforward marketing approach would be (a) show that other credit cards are doing something their target audience doesn't like, (b) build on their sense that this isn't ok, and (c) present the new card as a solution. Without ads they would likely still see uptake among people who were aware of the problem and actively looking for a solution, but mostly people would just stick with the well-known companies.
* Reviewers would be much more trustworthy. There's a long history of reviewers getting 'captured' by the industry they review, ex: https://www.fastcompany.com/3065928/sleepopolis-casper-blogg...
* Purchases of things people hadn't tried before would decrease, both things that people were in retrospect happy to have bought and things they were not. One of the roles of advertising is to let people know about things that, if they knew about them they would want to buy. But "buy stuff they don't need" isn't a great gloss for this, since after buying the products people often like them a lot.
This is just my guesses; I work on the technical side of ads and don't have a great view into their social role, and even if I was in a role like that it would still be very hard to predict how the world would be different with such a large change. Where does your picture differ from mine?"
(For 'saving the planet' I think a carbon tax would make a lot more sense.)