One difference might be that once a private company officially owns existing infrastructure, with no competition, they might not be adequately answerable if they fail to maintain it or charge excess tolls. At least legislators can be voted out of office.
“...they might not be adequately answerable if they fail to maintain it or charge excess tolls”
Here are the rates for the 407 ETR (private highway) in Canada, comes out to 35 to 50 cents PER MILE (the US gas tax is about 2 cents per mile, by the way). There have been lawsuits against the operator for gouging, but their contract is iron-clad. But don’t despair, in another 65 years or so, the ‘contract’ will be up for bid again.
http://www.newswire.ca/news-releases/407-etr-announces-2017-rate-schedule-608782365.html
Great model to follow...but what the hell, if we call it ‘capitalism’, then only ‘Socialists’, like myself, could object to it.