The law is whatever society decides it should be. There is nothing inherently rational about it. You'd have to accept some pretty messed up things as rational if you actually believed that.
1) The law is what a very small group of people decides it should be, and
2) Slippery slopes in law are a very real thing. Just listen to Supreme Court oral arguments. That's (supposedly) why it takes so much forethought and time to enact them.
American law for example reflects views and interests of small group of oligarchy, and not general public. It's been like that for quite a long time, to quote [1]: "The preferences of the average American appear to have only a minuscule, near-zero, statistically non-significant impact upon public policy"
[1] https://www.theatlantic.com/magazine/archive/2018/03/america...
My favorite in my current industry is how codified insurance costs are built into the system. You can't charge below X, because that would undercut the big players. So you have price floors, for no reason other than regulatory capture and payoffs.