What you all are doing is taking the letter and even excerpts of his letters out of context. It is just as I said. Beastie does this in her OP where she posts the Hotchkiss letter dated 1841 and then the comment about the location being healthful and uses that as some sort of evidence that Joseph was lying in 1843 when what she has done is ignore that the letters are 2 years apart and the land, by then, was indeed healthful.
Now it's my turn to assert that you have not read my posts. I have consistently noted the dates and also noted that there are two issues involved:
There are really two issues that ought to be separated out - the first is that in the August 25, 1841 letter Joseph Smith admitted to trying to persuade immigrants to buy land on what he knew to be a sickly death hole. To evaluate the morality if this act, no more information is necessary, because of this admission. We know that Joseph Smith was willing to endanger the lives of immigrants for financial reasons.
The second issue is when he used the "name of the Lord" to tell immigrants, in 1843, that the bottomland was the healthiest. This is where we need more information. If I find anything else, I'll let you know. I'll look up Cook's book.
So really, for me, the sole question is whether Joseph Smith was willing to use "the name of the Lord" and his influence as prophet to do what we already know he was otherwise willing to do - influence people to buy certain land, despite the fact that health problems were known to occur there. We can't tell from his letter to Hotchkiss whether he was using his religious influence to persuade immigrants to buy land in the sickly death hole. Given how everything Joseph Smith did was based on his religious influence, I think it's safe to assume he was, but it is an assumption.
Just based on logic, I find it unlikely that the bottom land was able to transform, in less than two years, from a sickly death hole to the healthiest land, particularly considering the above citation I linked that stated malaria (or fever or ague) remained a problem for many years. Certainly draining the swamp would result in improvement, but to improve so much that it was now healthier than the upper lands? I'm skeptical.
I've been using the term "two years later", but technically, it was 20 months later. 20 months for such a miraculous transformation, from the sickly death hole to the healthiest land in the area.
Neither Bob nor Jersey Girl have provided evidence to support their assertion that this transformation did, indeed, take place. I provided contemporary evidence that stated the illnesses continued.