I've read all the warnings about lecithin too, but the refinement process will denature anything there. Trace residues are usually compounds that do nothing. :)
The warnings about soy don't apply to lecithin, as it isn't the lecithin that makes Soy be a problem - it's the high amounts of nitrogen/amonia byproducts from digesting tofu, the preserved/processed version of soy.
As for rancidity, just check the expiration date and try to buy from a store that restocks its shelves frequently.
The *potential* issues are far outweighed by the benefits.
As a way to keep a bit of proportion when reading posts like these, remember you can eat a teaspoon of arsenic every day for two weeks before you experience any negative symptoms. The traces in lecithin would be measureable only to a microscope.