Overview
When someone comes up with an awfully bizarre idea, be careful about blurting out what you really think right away -- the person suggesting it thinks it's brilliant. Instead, try to view this nutty notion from a few different perspectives, so you can carefully and impersonally point out flaws. Suggest that there are quite a few downsides, and advise this person (very tactfully) to think this plan through a little bit more before revealing it to the rest of the world.