Another potential issue with the approach you outline is extortion. Maybe B finds X extremely harmful, and A is (nearly) indifferent between it and another option Y, or even also somewhat prefers Y to X. A could threaten B with X to get resources from B (say to do much more of Y with). I don’t think we’d want to allow this, at least to a significant degree, e.g. A shouldn’t do (much) better than both X and Y this way, and B shouldn’t have to pay (much) more than the resource value of the difference between X and Y according to A.
Another potential issue with the approach you outline is extortion. Maybe B finds X extremely harmful, and A is (nearly) indifferent between it and another option Y, or even also somewhat prefers Y to X. A could threaten B with X to get resources from B (say to do much more of Y with). I don’t think we’d want to allow this, at least to a significant degree, e.g. A shouldn’t do (much) better than both X and Y this way, and B shouldn’t have to pay (much) more than the resource value of the difference between X and Y according to A.