I like the concepts of “no harm no foul” and “what they don’t know won’t hurt them.” Unless you are like that Oregon guy that dam an entire creek, how would anybody even know that you have a rain harvesting system on your property?
This is what one could literally call "fake news".
So then it's mostly true, since the few laws that exist restrict the amount collected, limit it to non-commercial use and/or prohibit it from being used as potable water (because water has to be treated).
You're doing what you accused them. "I'm right, so nya-nya-nya!" Except that you're wrong.
Because rain falls onto the land, and the land belongs to land lord, not you. Stop stealing landlord's water, peasant