A strong argument would at least consider the systemic consequences of commissions, rather than just extolling the assumed virtues in a circular argument. What is their impact on product? On support? Engineering morale? On the customer experience itself? Just a myriad of effects not even considered here when commissions are looked at in isolation, the system be damned. It's probably very true that it's not plausible…
It's not a circular argument to point out that excellent sales people will take the commission job, while bad sales people will take the salaried job. All the things you mention (support, morale, ...) are second-order considerations -- the first order consideration is getting the best people.
As W. Edwards Deming said, "A bad system beats a good person every time."