Nobody is forcing people to buy early access, and they always come with a big fat textbox stating the differences to release. If there's a market for that, why not? Providing people the option to be beta testers for free, in exchange for early access and slightly lower price for product is fine, and apparently a lot of people think so. Certainly there are abusers, and Steam is trying to improve things.
The flip side is that when halfway through the development cycle, the dev decides to go a completely different direction and starts over with a radically different concept, now the people who bought in at the beginning don't have any ability to vote with their dollars and ask for a refund, which is problematic. So there are abusers on both sides.
More importantly, this change makes early access a whole lot less attractive and a whole lot riskier from the perspective of a potential buyer. As a result, I'd expect people to be a lot less likely to bite the bullet and give people money before something is complete or nearly complete. And I suspect that the people who do buy early access games won't be willing to spend as much money for that privilege because of the increased risk caused by this rule change. So creators are likely to get significantly less money by making something available in early access than they would have before this change to the rules — likely to the point where it doesn't even make sense to release something as early access until it is mostly finished, which completely defeats the purpose.
There's probably a middle ground somewhere, but my suspicion is that this will turn out to be a significant net negative for content creators, in spite of preventing a small number of freeloaders from taking advantage of it.
Also, if it becomes obvious that making things available for early access won't bring in a significant percentage of the final purchase price, I would expect most content creators to start making early access versions available through other vendors, either with a Patreon-like model or by making early versions free with the understanding that at some point, they'll charge for it, and only people who buy it will be able to upgrade past version 0.5 or whatever. And approximately none of those people will end up converting to paid ownership through Steam, so Steam will also end up making less money as a result.
So I'm having a hard time seeing how this is supposed to actually be a revenue-positive decision for anyone involved.