How? Do the police need a warrant to look at the pictures you upload to Facebook? What about if you put your DNA profile up on a giant billboard (GCAGC....), do they need a warrant to look at the billboard? It's illegal for them to come and take your DNA out of your body, but if you just upload it to some website for freely compare against and/or download, you are giving everyone permission to compare against it or download it.

I would never upload my DNA profile, but I have relatives who do. So I am not broadcasting the info, but other family members may.

I am generally alright with law enforcement using public information like this, but it could be used against me without me ever making said data public. So I find your argument invalid.

So lets say the police see your brother, and realize he looks suspiciously like a criminal they are looking for, so they come find you.

Your argument is that your brother's appearance can be used against you without you ever going outside, so it should be illegal for the police to look at people.

It is more of a question of resources. Why do they spend time ( and tax money ) trolling the internet?

In this case, if my cousin uploads her DNA, I am not giving it away and yet.. it is up for grabs.