If you're gonna call this a debate imp, at least contain your argument to the last 5 years. You keep citing "ghost stories" as a possible example of what could happen in the here and now. For every modification you make to your "what if" doomsday water scenario, I keep telling you that somebody smarter than you and I have already thought of it,..............and fixed it...................20 years ago.
One last point imp........
Belly pans. Again,.... if you'd ever even been under a new car in the last decade...you'd find it next to impossible to even see the freakin engine from under the car. A BMW ( and I'm sure a whole bunch of others) have a complete, full length, remove able belly pan under the car.
They do this for a slew of reasons imp, ol buddy,...From keeping road film, and debris from entering the engine compartment and contaminating/ fouling the components from underneath ( which directly contributes to how clean the drive train stays, and minimizes any damage from a piece of debris thrown up if struck) to Reducing the effects of aerodynamics on cars that are capable of 195 miles per hour off of the showroom floor.
What am I forgetting? I know that there was one more reason a new car has at least a cover under the engine....

it was right........here.....
Oh yeah!
Keeping road water spray out, and off of sensitive electronic equipment. ( like an ignition component)
The belly pans are so tight on a BMW. That when they leak oil from above, the pan traps it. ( and they always leak oil from above). owners are not aware of it, as it leaves no evidence of leakage on the garage floor. If the pan is that good at trapping stuff from coming out from above, I'm quite sure it'd be equally good at stopping stuff from getting up from beneath.