Advertisers pay money to serve ads not out of the goodness of their hearts but because they want to earn back not only their initial investment for the ad but a profit on top. Since they keep buying ads, it means that they are able to achieve this.
This means it should always be cheaper to pay for a service directly (avoiding all middlemen involved in the advertising industry) than to "pay" with ads. In the latter you'll not only still pay, but will have to pay more to cover the overheads of the advertising industry.
If folks were truly poor then they would be denied service since nobody would pay to serve them ads. Advertisers paying to serve them ads means there's still money to be extracted out of them, money they're better off just paying directly for the service they use.
Forcing poor people to be without their privacy whereas everyone who can spend pennies for digital services get to keep theirs also doesn't sound perfect.
Regulation is the best chance for well-functioning markets. I highly doubt we are going to be without advertisements.