You say you distrust government, but you propose to tax large corporations out of existence. The government would do that, who else.

What's worse, any single rule against large corporations will be worked around. You will have a loose association of just-the-right-size corporations. They will find a way to work together as one, while legally being many and each small enough to have small taxes.

Look at the recent software for rent collusion. Without an active powerful government to attack this new invention, they would claim there is no price agreement. Actually they do claim that. There is none formally, but the same effects are somehow achieved. If you want the government to be limited to applying some simple rules, this would go unpunished. This requires the government to adapt and use judgement and discretion.

You need an active powerful entity to balance the power of economic behemoths. We don't appear to have any other way, yet. I think the key is balance.