@peterb @dosnostalgic @lunarloony @Tijn
Monopolies are an overwhelming problem in many walks of life.
I think someone in another branch of this thread already made the point that the fixes are often appalling (e.g. electricity resellers, or the UK competition and markets authority's obsession with stopping Microsoft to the exclusion of deterring other harmful monopolies), but that doesn't mean that the problem isn't doing harm.
The utilitarian position for consumers in particular certainly makes Valve an excellent "lesser evil" example in the corporate world, but that doesn't really help the devs who effectively have no choice but to put their games on there at a mandatory 30% or be effectively invisible to the market they need to sell to.
I don't have a solution here (yes, capitalism is structurally bad, and the People In Games Revolutionary Army is unlikely to be a deciding factor in the immediate future), but the people trying to run an entire small gamedev business under these conditions certainly have good reason to be peeved.
(Which is why I mostly work as a contractor for other people.)