Pressure Regulator

well, that is not true
the carb is set up to withstand a certain inlet PSI, most times 8 PSI
the float can only withstand 8 PSI to close the inlet of fuel
if his line pressure is higher then that, the float, when rising to the top, will not be able to close the intake, and the bowls will flood
then fuel will drizzle into the throat of the carb and the car will run like crap

to stay with your toilet bowl analogy, your tank would overflow and water would pour all over your bathroom floor, next thing you know, the wife walks in, slips and falls, knocks her head on the toilet bowl (chipping it) and you're spending the rest of your life taking care of a woman on a respirator
You only read part of it. Use an appropriate valve and your toilet won't overflow whether it has 20 psi on it or 120 psi on it. It will fill more slowly at 20 psi than at 60 psi.

And I disagree on the 8psi. For most carbs we use here, 8 psi is pushing the limit of what the inlet valve can hold off - the bigger ones of course are worse.