You want people to be able to contribute anonymously. You need an upvote/downvote system to be able to organize discussions. You want to keep bots out. Bots can generate comments indistinguishable from those produced by real users. Captchas are not enough, it's an endless race. Most people don't want to deal with crypto and blockchain stuff because it's complicated.

THEREFORE

Someone sell physical free speech coupons. Instead of paying 25 cents to buy a newspaper, you go to the newsstand and buy a bunch of coupons. With cash, wearing a mask if you want. Some newspapers or publications could also include free coupons.

To comment on a website using this system, you spend a coupon by typing its number or scanning it. Better, you have to scratch it first.

Your agreement with retailers says that they can't sell bulk to third-parties, they have to sell to individual humans.

Also, this creates a contractual relationship between you and the publisher, they can't delete your comment if it's legal or make bullshit changes to ToS. Make sure coupons are valid for at least a year.

This supports hosting costs, and I think it would make botfarms much more difficult and costly to operate.

Is this a dumb idea? Is there a weakness?

If not, please get some entrepreneur to implement something like this.