In perfect price discrimination, all mutually beneficial trades take place, the natural monopoly captures 100% of the surplus, and pareto efficiency is achieved.
However, I've read various sources that mention that, despite this, economists still advocate various taxes, regulations, or nationalization to "fix" the monopoly problem even in theoretical cases of perfect discrimination. Why would these things be advocated if pareto efficiency is achieved?
The only thing I can think of is that, while the lack of competition doesn't remove the incentive for a monopoly to innovate, it hugely slows down the rate of innovation, which would essentially rob society of potential improvements.
Is there anything to this logic? What inefficiency would exist if not pareto inefficiency?