It's not that businesses have a fundamental right to buy people's attention. It's that people have a right to sell ad space that they own to other people to show messages on if they want to. I dont think its right to tell (example fake website) plumbersupport.com that they cant accept $500 from a plumbing saas product to put a banner ad on their site because advertising is bad.

This kind of situation is win-win-win.

The plumbing website makes money from the ad - supporting their operations so plumbers can keep a good source of plumbing educational content.

The SaaS company gets to put their product in front of users to look at and consider buying.

The users get to see a potential product with no obligation that they may have not ever heard of before.

So basically you're saying businesses have a right to sell peoples' attention. Of course for every seller there's a buyer but I do kinda see that how this framing would make a difference, ethically, for some.