I fully support their right to change their licensing, and I understand they may not have thought through the implications of their license -- and I empathize with that. I also empathize with criticism that Amazon isn't doing a great job of supporting the ecosystem that supports them, it would be nice if they did more. And it goes without saying, but I also strongly empathize with the frustration about the borderline trademark infringement that's happening here. That's a completely separate problem.
But I don't like the implication that Open Source licenses are a legal technicality rather than a specific philosophical choice to allow reuse. People don't need to feel guilty about following Open Source licenses, the idea is to encourage reuse -- even by corporations.
We do harm to that movement when we try and backtrack from that philosophy or say, "sure, you have the legal right to reuse the code, but we're going to try and implement social/technical barriers to you doing so." There are plenty of decent source-available licenses projects can use if that's their intent. They carve out exceptions for small-scale reuse while trying to limit companies like Amazon from capitalizing on the ecosystem. And maybe more projects should use those licenses since they more accurately reflect the outcomes that the authors seem to want. There's nothing wrong with having projects that allow only small-scale reuse.
But if someone releases their project as Open Source I'm going to treat it like Open Source, because that's what the movement is about, and trying to reverse the legal progress we've made by constructing new moral barriers in front of reuse is harmful to that movement. When we say that people have a moral right to reuse, adapt, and share our code, we mean it.