If you assume (as many do) there is a relationship between the stock price and the profits of the company, then corporate taxation serves to reduce profits, reducing the stock price. So, instead of rising to $500, it may have risen to $750. The forgone (and invisible) $5 million of appreciation was the loss due to corporate taxation.

(Obviously, the above is too simplistic to actually rely upon, but that's how corporate taxes reduce investor returns, effectively resulting in double taxation in many people's mind, including my own. I still believe that's part of the reason LTCG are and should be taxed at a lower rate than ordinary income.)