> You're selling part of the nation's infrastructure, that was paid for by taxpayers, to now be exploited for profit

Maybe. If it's taxpayer funded infrastructure, it doesn't perpetuate itself by self determination. It must be maintained with more tax dollars.

Assuming the cost is equal whether it's privatized vs. state-owned, then it all boils down to a matter of ideological preference. Some object to others making a profit off of a public good. There may or may not be merit to those arguments, but they're completely orthogonal to whether or not there are costs associated with their maintenance, because there always are.

The taxpayers always end up paying twice.

If costs are equal, the private for-profit entity is more expensive, because it wants to make profit. If it bought the infrastructure, it wants to recoup that investment.

Apologies. I intended "costs" to mean "costs to consumer".

Sure, if the costs to the consumer is equal, it doesn't matter much. But I think that's unlikely. In a privatised versus nationalised comparison, I think the costs to the consumer are either going to be higher if it's an area where competition doesn't work efficiently (monopolies, duopolies, cartels), or lower if it's an area where competition does work efficiently (a transparent market with many suppliers).