Let me start off by saying that I think most startup compensation is downright bad for employees, compared to FANG alternatives. I would like to be a startup founder one day, but I realistically can't see myself as a startup employee.
That said, I don't think Gumroad did anything morally wrong here. The layoffs were absolutely necessary, because the company would have gone bankrupt without them. But it's false to say that this caused employees to have no equity. Even if you get laid off as a startup employee, you can still choose to exercise your options and hold on to the company's equity, if you think that they will eventually be worth $100M. No one misled the employees about the company's future. They saw that the investors were pulling out. They saw that the engineering team was getting shredded. And they made the very reasonable assessment that the company's equity isn't worth the cost of exercising their options.
Blaming Gumroad for employees not having equity, is like blaming AMD for their previous employees selling off their stock during their near-bankruptcy days. Any company can and will go through dramatic reversals of fortune. And whenever there's such a turnaround, there is bound to be people who missed out on the upside, because they didn't continue holding through the dark times.