I suppose I need to explain my position. Steam is an Internet shop, where people buy software (with all the legal responsibilities of involved sides and so on). Demo is incomplete version of software. Steam's added bonus - you can buy incomplete product (Early access) to support a developer, in case dev can't have resources to finish product on his own. The only reason Early access is exist is exactly that, give money to developer for finishing. Steam is not a crowdfunding platform. That was definitions for explaining.
Look at PinkCake. He finished "Acting lessons", then published it in Steam. People bought his game, it brings money to dev for his good work. After that he published his current WIP "Being a DIK". Price is close to "Acting lessons", game is still in development, every update goes simultaneously in Patreon, Steam and any other platform. It's Early access, dev don't have enough resources and using Steam function to do have what he needs. Anyone who buy BaDIK, got current version with any future updates. Beacause that anyone already bought BaDIK, he/she is a current supporter and have a full right to have the most of the product. Bruni Multimedia does the same thing, first the Early access, now game is finished and everyone who bought it on Steam have not only full version of the game but every subsequent updates. I know what I am speaking about, I actually bought "Acting lessons" and "General practicioner" (not BaDIK, but for a whole other reason). Philly games is the third one who did the same.
So, what I am talking about. Three devs, good devs I might add, publish their games in Steam as just another platform, totally equal to Patreon or another platform for earning money for their work. Steam buyers have the same version of software as Patreon users, they are totally equal, 'cause all of them bring money to dev. Steam users are not worse than Patreon users, they just pay for product their real price, not worrying about is dev will finish the game or not. Yes, it brings less money than Patreon scheme, but that's how real gamemaking work. Big companies paying for a few years to their developers in hope they make good product that bring profit. And sometimes they fail. It's just a risk of making software. And if you, as a developer, diminish actual buyers (users of Internet shop) comparing to people who has excessive money (any crowdfunding platform), you just show people where your interests are. And that interests usually do not include good software. And that's where milking goes.