For example:
1) If someone glances in your window as they walk by your house, that's fine. If they stand there all day, they're probably guilty of stalking, a crime.
2) If one person is holding a protest sign in front of city hall, that's legal. If a thousand people do it, that's a protest, which in most cities is a regulated activity requiring a permit.
3) If you pour your morning orange juice out in a storm drain, that's probably legal. If you pour thousands of gallons of OJ into a storm drain, you're breaking environmental laws.
4) If someone drives by a street, that's fine. If they go back and forth down it, they're cruising, which is a crime in many cities.
5) If you give a friend $100, it's an unregulated gift. If you give them $20k, then that's regulated by tax laws.
6) If someone sells a stock and buys it back, that's fine. If they do it tens of thousands of times in a minute, they may be breaking securities laws.
7) If you bring $1000 into the country, that's an unregulated event. If you bring $100k, it becomes regulated.
8) If you access a web site with an automatic tool, that's fine. If you access it a thousand times a second, that's a DDoS attack, which is a crime.
9) If you cut a tree down on your property to sell the wood, that's fine. If you cut hundreds down, then you're running an illegal logging operation.
and on and on.
I totally don't buy the argument that it's unreasonable to forbid or regulate the case of collecting license plate numbers based on it just being a different quantity of something that's permitted. Laws use quantity as the basis for drawing the line between legal/illegal or unregulated/regulated all the time.
However, in this point no such distinction has been made, and thus they should be treated equally. There is clear law on the "low quantity" case, and no distinct law on the "high quantity" case - so the same principles should be applied even for thousandfold or millionfold increases unless/until the lawmakers (not the courts) draw a line somewhere.
I'd rather prefer if everyone was permitted to do this at all scales, rather than risk restrictions on what people can do with their minds and devices with stuff that they can plainly see - it's similar to various restrictions on recording police officers in action, so as "to protect their privacy".
The government will do their thing anyways (as Snowden showed us), so if any restrictions are implemented then they will only restrict us, but not protect us.
I'm aware of the copyright legislation that applies to copying of data compilations - but those restrictions don't apply here, where people are [re]creating databases from independently made real world observations.
Don't make problems simple and obvious when they're not.
A single fact about a person at a particular place is not much more useful than knowing the placement of a single letter in a word. But if you know the placement of several letters in a word, you can guess the word - and that has a whole bunch more information [1]. Similarly, know several facts about a person's path, more information comes to light that is not evident from single facts alone, in a way that the whole is greater than the sum of the parts; place of work, school of children, likely friends, relatives, partners, potential medical issues, possible infidelity.
The issue you're getting at is a philosophical issue related to the sorites paradox on one hand, and the zero marginal cost of duplicating information on the other. The former is somewhat related to the issue at hand, but the latter definitely isn't.
[1] Semantically, not by Shannon, for the autistic nitpickers out there.
I hate to say it -- because it's probably irrelevant from a legal perspective at the moment -- but this sounds exactly like the fallacy of the beard to me.
(edit: not to accuse you of committing this fallacy, just felt this was important enough that it should be highlighted)
If I have unconditional permission to read books from library, then that allows me (I don't need any extra permission) to use what I read to create a library index - even if you explicitly don't want me to have such an index.
And the public information permissions really are unconditional - what I see in public space is public info. There's no "... unless you write it down" or "...unless you plan to keep that data forever" or "... unless you don't gather too much" or "... unless you tell it to others" or "... unless you profit from it" or "... unless you make interesting conclusions from the raw data" - it's just that, public and unrestricted.
Once I have a legally obtained fact in my mind or my computer, I'm allowed to do pretty much everything with that knowledge, barring very specific exemptions such as blackmail or insider stock trading.
I'm disappointed, as I was hoping for some sort of informative argument, as someone with no strong opinion either way.
If I don't need your permission to look at your car's licence plate on a public street and write down when and where I saw it, or simply take a photo of said licence plate (as photos currently include timestamp+location) - then the situation doesn't change in any way and I still don't need your permission even if I did the same for a thousand cars this morning, and my buddies did the same thing for ten thousand cars more.