The OP explicitly answers this: go back to pre-80s antitrust policy. Companies can be bought and sold but not if it creates concentrations of economic power that allow them to dictate prices to vendors or customers.

But "corporations are people" and those types of markets have closed since 1865 in the united states.

Why do you present this as a binary to agree/disagree with?

But we can't have that because then we'd be wasting potential profit. /s

I think the really important question is HOW this will happen. If you mean for the state to buy them at fair market value, nobody will object to that, not even if it closes the door to private equity.

But that's not what you're talking about, is it?

How about doing what America used to do? Provide seed funding for a new fire truck company in trade for condictions. Can we agree to do that? Fund 3 companies to make fire trucks, fast-track whatever certification and approvals they need. Create the companies we need, risking (and in fact expecting to lose) a bunch of the capital used for this.