My personal opinion is that the truth lies somewhere between. The snakes may have gotten to the everglades from hurricaine damage and from idiots letting their snakes go. I live in Missouri and we just found out a nearbly man-made recreational lake has two large alligators alligators swimming around that they are trying to catch. I know how easy it is to buy a baby alligator online. Surely someone bought one and later realized they couldn't handle it...and let it go. If I was irresponsible enough to do something like that I would think I would still be smart enough to be sneaky about letting the alligators go. You can stop the car by the lake at night, somewhere out of the way with no other people...it would be a cinch. I don't think anyone is dumb enough to pull over on a busy road in broad daylight and drop-kick a 20-foot snake out of their trunk.
Maybe the hurricaine contributed a little or a lot of the snakes...but I know there are a lot of irresponsible pet owners that just let them go.
I have little kids and I don't want my neighbors owning potentially lethal animals (whether they are lions, bears or burms) IF they don't know how to keep them. I think a workable law would allow licensed keepers to keep the animal if they passed regular inspections looking at their cage setup...