Too often laws get misapplied. Disease is a worry in some cases, but clearly not in this case - the vet is the first place this deer went. Some people see baby animals alone and wrongly imagine that they’re abandoned or sick. Well, in this case the fawn was clearly sick - legs that needed casts to straighten them.
Wisely, the possibility of euthanasia was dropped the day after it was impounded.
As for the general issue of raising wild animals... as long as the animals are properly taken care of and kept on the owner’s property and are not endangered species taken from the wild - where’s the problem? (Or maybe that’s part of it - expense of checking to see if they’re properly taken care of?) It may be dangerous to the owner, but that should be the owner’s choice.