What if it's a disease you just discovered you have, and you don't necessarily have all the information yet? Should you be targeted before you've had time to look into it, much less come to terms with it?
What if you have a child with health problems or are part of a pregnancy that has problems? Would you want companies that might take advantage of the situation to be able to target you?
What if you've just been turned down for a job? Should a for-profit college with poor qualities be able to target you right afterwards?
There are many times when we find ourselves in an altered state of mind (even if slightly) where we are more susceptible to our baser emotions. Do we really need to engineer a system so companies can better identify when we are in these states for their benefit and to our detriment?
It's fine if someone wants to knowingly trade their information away for some benefit, but they should be able to see what they are trading away and make an informed assessment. What we have now doesn't really allow for that, and once it's out there, it generally has little to no value later (once you're marked as an ex-con, good luck getting that our of everyone's data sets).