Capitalism is about future profits, by definition. I can't invest money in Apple in 1997. I have to invest it today, and my only concern is what happens after that investment. The Uber boarding kicking him out is entirely a capitalist reason. They've invested money, and his presence will (they believe at least) negatively affect the return on that investment going forward.
Your only concern may be what happens after an investment but you'd be foolhardy not to take past performance into account. Undervalued (Apple in 1997, return of Steve) is one thing. Throwing good money after bad is another.
$2.8B is just a ton of money to lose and for a startup it's insane (thinking of Amazon but Uber's losses dwarf Amazon's early losses). Frankly, I think the board is using this as an excuse to do now what they should have done a couple of years back. Boards are human. They aren't homo economicus incarnate. Ascribing rationality to the outcome of a board meeting because capitalism makes no sense. Really, they lost $2.8B last year.
No one is suggesting that. When people say "this is capitalist of the board to do" they're talking about the individual board member profiting from a successful exit. Put more simply - investor puts $1 in Uber on day 0 and expects to make $100 on day 1,000 and makes a $99 profit. They're axing TK because they want to make their $99 return on investment.
And Travis was not held accountable by a legal system - his investors (i.e. capital) asked him to step down.
I think we're all saying the same thing, it's just your conclusion is incorrect.