first ask yourself the question: will the private sphere do the job better? if the answer to this is no, ask the next question: does it have the potential to do it
worse?
"Private" roads benefits:
No need for new taxes to finance the bot projects.
Having the same firm in charge of construction and maintenance provides better incentives to build a road that lasts longer.
Private firms usually are better at managing and more efficient than state-owned companies.
Cost-based tolls are easier to justify to the public when infrastructure providers are private.
Those who benefit from the infrastructure pay for it.
In stark contrast to public provision, the bot scheme uses the market mechanism instead of central planning to screen projects, which reduces the probability of white elephants.
first there is the idea of "bot projects" and taxes which is somewhat misleading. ask people if they are okay with their taxes paying for roads, and you'll be hardpressed to find anyone horrified by it. roads are important and if a private company does them, they can do shit like lock out access to certain people if they want (much like how a driveway is your property, so you can seal it off with a gate).
secondly, the concept that the same firm doing construction and maintenance will result in better roads is wrong. I worked in road maintenance for a year (I've only last night realized how much ridiculous experience I have on GW, everyone probably thinks I go visit the UN and rap stars while paving roads and working hospitals) and they do a damn fine job of it. more importantly, why would it result in better roads? tell me, if a meat company kills your cow does that also mean it's going to be good at grilling it? a stretch but you get the picture. they are two different ideas and there's no real correlation between building a road and maintaining it as to suggest it will be better under one roof.
private firms are not better than state owned operations. this is a lie libertarians like to trot out. I said this in another topic, but Charles Goodsell's infamous polemic, The Case for Bureaucracy, does a full and indepth study and confirms that there is no bias in either direction in regards to who can run aspects of industry better.
the justification argument is so laughable I'm not even going to seriously address it. people will feel better about tolls if they know it goes to KFC instead of GOBMINT. please.
the BENEFIT argument is bizarre. everyone benefits from roads and via taxes, everyone pays for them. doesn't this argue the other side? the other way to see this is some "people who maintain roads will get money to maintain roads" which is what happens anyways, there's no extra incentive. road maintenance workers aren't LAZY.
the last argument about BOT contracts ignores that there are ALREADY problems with BOT style contracts. when I worked RM we had a chemical sprayer company that we hired out for a road repaving, but we discovered quickly that it was eroding asphalt because of a formula switch. they refused to reimburse the state. were this completely privatized, no one would have said anything and the road would break down earlier. also the idea that this won't create white elephants may be true, but it will create investors that might want to cut and run and leave a major highway full of potholes or maintained poorly.
we use BOT contracts for initial construction sometimes anyways, and I just provided one example where the bureaucracy had to watchdog the private enterprise; privatizing roads would reduce that watchdog to nothing and we'd end up with shittier roads by far.