I would go a step further and say that it should not be a stock purchase but partial nationalization. The government is not getting shares that will be sold later. The government is getting a right to appoint part of the board of directors. Every time the company issues a dividend, buys back stock, or engages in other activities to return value back to the shareholders, a proportional amount of money must be paid to the treasury. It only makes sense that if a company is so big that its failure is going to hurt society as a whole, it should be owned by society.