Interesting definition of economic rents. Much more constrained than the generalised rents == unearned profits. It's definitely given me something to think about. However, I have to disagree with a number of your points. The assertion that rentiers and more generally, the existence of private economic rents, do not impose costs elsewhere is not correct. In a direct sense, they reduce the general wealth level around them because that is precisely what they are extracting from others.

In addition, privatised rents distort the allocation of capital and labour towards the direction of wherever that rent exists. This is bad for a number of reasons: productive inputs are not being put to their most productive use, often large proportions of a community's or country's productive capacity is being employed to enrich a relatively small rentier class, other non-rentier businesses are either hobbled or destroyed by higher input prices and if the rent is attached to an exportable commodity (e.g. iron ore, coal, oil), export facing businesses suffer due to relative appreciations of their domestic currency.

It's interesting you bring up raw materials: I assume you mean natural commodities like iron, coal, gas, oil etc. These are the classic example of rent-generating commodities that make a small number of people very rich, while severely distorting the capital structure of an economy. For example, take a look at: https://en.wikipedia.org/wiki/Dutch_disease. Ironically the Netherlands has probably some of the world's best policy in this regard, mainly focussed on their successful oil export industry. They ameliorate the effect by a combination of high rent-recovery taxes ~%60, a significant degree of nationalised production and a very well-funded sovereign wealth fund.

And it may be true that retiers may, in some circumstances, be the main beneficiaries of increased demand. However, this could be said of many businesses. I don't think this is the primary issue. Although it sounds a bit trite, the primary issue is that rentiers enjoy unearned private profits. So when a local council builds a nice park somewhere (with public money), nearby private landholders get to privatise a significant share of the benefit economic via increased land-rents (capitalised as higher private land prices).

Although it doesn't sound 'so bad', this kind of system can fuel very damaging economic behaviours: notably it can encourage speculative investment, lead to inter-generational wealth concentration, and it can severely distort the political economy. For instance, a land developer, fortunate to inherit the lucrative family business, can suggest to one of his long-time family friends, an influential member of government, where the government should locate that new train station they're planning to build (co-incidentally near some land he has been 'banking').

He might also provide his views that the government should tighten up on zoning laws (you know, to ensure family friendly suburbs), and that the government should slow the pace of its land-release programme (you know, because there's a glut at the moment and we need to combat urban sprawl). And he'll be listened to, thanks to his family connections and inherited wealth (a portion of which he donates to various political parties).

Wow this turned in to a bit of an essay. Just one last thing: I found your last paragraph very interesting. It's an area I'd love to see given more focus by academic economists, given the mainstream view appears to have whittled things down to just two factors of production: capital and labour. Perhaps we're trying to push a number of square pegs through a number of round holes here...