The question made me interested, so I did some Googling. Here are some interesting arguments/quotes I found on the Straight Dope's message board: I was taught, only a few years after it became law, that it was done by the Republican majorities in both houses of Congress as a form of spite or revenge against FDR.
And Nephrotic Syndrome is always accompanied by serious edema which is observable swelling from fluid accumulation in the body. With damaged kidney function, it cannot excretes wastes and extra fluid from the body and a large amount of fluid will pile up in the body, thus leading to swelling.
In these diseases, edema occurs primarily because of the body's retention of too much salt (sodium chloride). The excess salt causes the body to retain water, which then leaks into the interstitial tissue spaces, where it appears as edema. Medications also can cause pitting edema. The most common local conditions that cause edema are varicose veins and thrombophlebitis (inflammation of the veins) of the deep veins of the legs.