The implicit argument #5 is that a lot of people would be upset if corporations weren't taxed, because it wouldn't be "fair".

I might be wrong, but I think the system is currently structured such that corporate taxes are mostly a sham anyway; when they pay out dividends, those are taxed at a lower rate to make up for the corporate tax. This is probably anti-progressive because poor people aren't incentivized to invest in businesses, as they'd be effectively taxed closer to rich people rates.

Really, a surprising amount of screwy and circuitous things in our civilization are a direct result of income taxes.