In most places they are legal, mainly because nobody knows what they are. Most people are very unequipped to deal with them as pets. Their needs are similar to guinea pigs, and most people don't bother taking care of their guinea pigs very well.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry