Why Do People Get Offended When You Set a Boundary?
A boundary takes something away from somebody, and losses register in the brain as attacks. The reaction arrives because of: 1) loss aversion, since access they used to have for free suddenly carries a price 2) reactance, because being told no triggers a push against the limit itself, completely separate from whatever the limit is about 3) the first reaction being a test, since a new rule gets checked for whether it is real before it gets accepted. The offense is not evidence you were wrong. It is evidence the boundary changed something.
What is actually happening
They lost free access
Losses land as attacks
The first reaction is a test
Hold it once, quietly
How the pushback moves
Hold it one time without explaining and watch what the second reaction is.