The pro-proof-of-stake argument is that every other system is inherently already like that: For example with proof-of-work, the richest can already afford the most hardware which gets them the most earnings. But actually with proof-of-work it's even worse, because it is a non-linear relationship as to what kind of mining hardware you can afford (richer can afford exponentially more efficient hardware). So proof-of-stake is actually better, because at least it's linear.
That's equivalent to saying that you can invest in a cloud mining operation or pool funds with friends to by a larger mining device than you otherwise would alone-- in both cases you lose control of your influence in the consensus and essentially end up paying someone else to centralize the system more on your behalf.
