It is ICE (not the police) that is harassing people, and why should anyone need to carry proof of citizenship?
Further, even if you have proof of citizenship, what makes you think you'll be asked for it, rather than just being shoved into an SUV? There have been numerous citizens that were detained:
And being detained may be for the fortunate case: many US citizens have been deported. Without trial. With an opportunity to show evidence that they are in fact citizens.
This is why protecting due process for non-citizens, illegal or otherwise, is important: if there is no due process, then the government can simply claim you are not one, and ship you off to who knows where.
