I learned that somebody already did such thing: http://stopice.net/ and it existed before this app even.

stopice.net? Yeah that looks like much safer alternative to iceblock

I think it might be simpler.

All the app could do is to report location of the user to ICE.

While people might be interested to show up to ICE raids, immigrants might also want it to know places to say away from.

Since the app is on the phone the location can be tied to the phone number and since they are going after documented immigrants they might have phone numbers from their applications.

I think this should be a mobile website instead of an app is the goal was privacy.

The problem with phone apps is that they already have access to personally identifiable information.

I would much prefer this was a mobile friendly website.