> if the project isn't economical after accounting for what it would cost to buy up the necessary property at market rates--which is to say, rates the actual owners will voluntarily accept without any threat of coercion or eminent domain--then it simply isn't worth doing
This sounds great on paper, but in practice it tends to break down. Consider, for example, building a highway. The road is gonna have to go in roughly a line between point A and point B. How much is that land worth? Since there's not a lot of flexibility as to where the road can go, there's no competition, and the owner can basically charge anything imaginable; there's no notion of a "market rate".
While my example was a highway, this applies to pretty much any transport infrastructure, and this exact scenario has actually happened in the case of both the Texas and California HSR projects.