But we all life with boundaries and we cope just fine. Why should this street in front of my house have a 35 MPH speed limit? What is special about 35? Why not 36? Why not 34? Who is to say that one is better than the other, so let's not try and all and let everyone pick their own speed.
Just as it would be possible, but stupid, to invoke slippery slopes to argue there should be no speed limits, invoking slippery slopes to argue against any regulation is a cop-out. Why not advance a real argument vs just arguing picking the optimal boundary is impossible?