In a company with a well known lack of traditional corporate hierarchy, who does the firing? I'm genuinely curious. None of the reports I've read have mentioned it, which leads you to assume Gabe. This would imply an informal hierarchy.
Having a manager fire you gives you a lightning rod to point the feelings at, rather than an entire group of people.
There are generally 3 types of job loss:
1. People who are unethical or obviously toxic. Here, management can step in and fire the person without much blowback. If someone steals, or is a direct threat to your culture (e.g. he starts playing politics and trying to set himself up as the executive empire-builder you don't want) then it's not very controversial.
2. Good employees who run afoul of political nonsense or parochial managerial politics. This is what companies like Valve are trying to avoid, because it poisons the culture.
3. Layoffs for economic reasons.
I assume this is a case of #3. The CEO needs to explain what happened, why it happened, take responsibility for the decision, and assure people that the company will be better after the change than before.
Comment sections are essentially infinite, and if the comments are good, I don't see any reason to tell him to stop. However, if the comments are not insightful/interesting, that's another story.
Another element to the art of layoffs is that you get about one shot every 5 years. One large cut can be painful, but it's not damaging to morale if it's well-justified by business or economic concerns. If you do a series of small cuts, that's when you get people paranoid and the alliances and intrigues start to form.
So, I think the best way to do a layoff in a Valve-style corporation is this:
(1) Fair severance, including career support (positive reference, right to represent self as employed). People will find out what kinds of packages people are getting.
(2) CEO communicates the decision to the whole company and takes full responsibility. No mystical "calibration scores" or HR indirections. He gets up and says, "This is what I did, and here's why I had to do it." I'm not talking about traditional hierarchy, but "buck stops here" leadership. That's needed when layoffs are happening.
(3) Unless the people actually are being fired, explain that it is a layoff and that the people will be eligible to re-apply when you start hiring. (Most won't come back, but this lets the rest of the team feel better about the whole thing.)
(4) Err on the side of a larger layoff, because a series of small cuts is more damaging.
(5) Impose a hiring freeze externally, but keep internal mobility as it is. Many companies impose internal hiring freezes during layoffs and that's actually more damaging.
ETA
(6) Make it very clear that these aren't performance-based firings. The worst is when a company tries to depict a layoff as performance-based. Layoffs are understandable, but trying to depict one as a performance-based firing is being a dick.