> but its pretty self-evident that the effect on actual prices is dependent on price elasticity of demand in the markets for particular products
Of course, but there's still the "minimum profitability" that a business seeks to have. Suppose three firms compete to sell widget X, and consumers are willing to pay up to $10 for it, but the companies sell it at $5 due to competition (it costs $4 to make and distribute). Then the price is determined by supply cost + reasonable profit, determined by competition. If the government removes part of that profit, they'll raise prices accordingly, and sell for $6 instead, since that's still within the demand price elasticity -- otherwise the firms would decide there wasn't enough profit and get out of the business entirely.
> No more than taxing labor income... is really taxing corporate stockholders
The difference is that taxing labor income can be intentionally progressive, which is widely believed to be a good thing.
> But taxing high salaries is "regressive"
That just doesn't make any sense -- words can't be redefined like that. The very definition of progressive taxation is taxing high salaries (EDIT: incomes) of individuals at a higher rate than lower ones.
I understand your overall argument -- it's certainly debatable to what extent you believe corporate taxes to affect prices, vs to what extent you believe personal income tax to affect market salaries. But that doesn't affect the point I was making, which is that corporate taxes are ultimately passed onto people, and that this is not done in a progressive way. But by taxing people directly instead, this can be done progressively.