Put it this way, if the standard theory of why capitalism beat Soviet communism is that competition created better products etc. none of that requires that the goal of firms is to create better than market average returns to shareholders rather than the goal of firms being a) earn sufficient profit to continue to exist b) benefit consumers c) benefit employees d) benefit shareholders. Yes shareholder would prefer to invest in companies that prioritize them over all else, but why should we the public not say “that’s not an acceptable charter. We don’t want feudalism to happen again, so we are not allowing firms to prioritize shareholders over consumers.”