Starting Monday, millions of people who have avoided colon cancer screening can get a new home test that's noninvasive and doesn't require the icky preparation most other methods do. The test is the first to look for cancer-related DNA in stool. But deciding whether to get it is a more complex choice than ads for "the breakthrough test ... that's as easy as going to the bathroom" make it seem. On one hand, the test could greatly boost screening for a deadly disease that too few people get checked for now. On the other hand, it could lure people away...