Well no animals should be let loose in area that they are not native to. Aswell for the people that cant care for there animals and let them loose there are 2 things. 1.this is why you need to consider the full life span of the animal before you buy it. 2. There are enough reptile lovers out there that is for some reason you cant look after them you can always give them to someone that will(for free).
You say that there are lot of herps that have been introduced and are not breeding but how do you know? Just cause you dont see it doesn't mean its not happening. Look at my area, we have massassaga Rattlers but do you ever really see them? NO, but just cause they are rare to find and see doesn't mean they aren't out there.
Over all I think its a bad idea introducing animals were they dont belong. Look at Austraila I believe it was the rabbit that was introduced there and they just took over and ate everything they could .
IMO BAD IDEA.