I'd like to add a bit to your comment. I certainly agree that negative prices in this context don't mean anything remotely nefarious, but part of your comment suggests that "it's all consensual contracts" is a sufficient ethical justification for a system — which may or may not be what you actually think — and I wanted to touch on that.
Markets come in all shapes and sizes, and in reality you can't write up any contract you like — nor should you be able to. Indeed, electricity markets must be tightly regulated due to shared infrastructure, which is an example of the fact that these markets don't arise simply from the application of a fundamental "allow people to enter into whatever agreements they like" principle, but rather requires pragmatic _design_.
Ultimately, we, as collectives, decide what the rules of the game are. In the case of electricity, the need for innovation and flexibility to decarbonise the grid are perfectly acceptable justifications for adopting market solutions (the only real alternative being to allow the State to monopolise the whole system, which would come with its own serious and disruptive trade-offs); but ultimately, this is a _system_ that we decide on, and it doesn't arise out of natural rights, and systems can be more or less well-designed. I think you touch on this in your comment as well.
Markets aren't evil, but nor are they naturally good. They are a tool in our toolbox for constructing resource allocation systems. And the success of a system, and indeed _the_ system as a whole, must consider all the interlocking economic and social consequences — and it's anxiety about those that the "late-stage capitalism" trope really reflects. It's not something to dismiss altogether.