So, the reason that it is not harmless is that 'cops' are already tapping this data?
The real answer for this is....
.... you shouldn't be worried unless you have something to hide. The Police are not going to routinely get every single person's data and decided if they are where they claimed to be.
On the opposite hand this can also be a saviour for someone that is blamed for something and their only alibi happens to be that they were in such a place a such time but didn't have anyone to corroborate the story. Then the data from their iphone is the perfect witness because it cannot tell a lie, it was where it reported it was according to GPS data.
Why the blazes are people getting so paranoid these days about data collection. So what, it is now done covertly.
This same information can also be used by the Telco's to decide where extra towers need to be set up to improve service.
There are far more positives that there are negatives that can arise from this collection of data and I will not get trapped in this paranoia.