Do you think people should be allowed to own certain snake species?

Well the vast majority of snake species are harmless, and I wouldn't ever condone keeping a venomous snake as a "pet". I've been bitten twice this week, by a couple of defensive younglings. A little peroxide and that's that. I don't think the dangerous aspect is really a part of it, almost all of the popular pet snake species are all but completely harmless to people. But, as you said, in an ecosystem that has evolved without snakes, they could certainly eat allot of animals, birds and small mammals in particular. All you have to do is to look at the effects over the 70 or so years since the brown tree snake was introduced to guam.