As I remember, Don Bluth himself stated that original Sharptooth wasn't villain at all.
the same we can say about all other sharpteeth.
Creature becomes evil when they do things beyond simple nature actions. Ozzy, Strut, Pterano, Rinkus and Serra showed us that well.
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More thoughts about Sharptooth and Red Claw gang...
Sharptooth, besides his natural hunger, wanted to make small revenge for his damaged eye. Hmm, does it make him evil?..
Red Claw... As I understand, he and his fast biters imagine themselves as the most important persons in region, so they banish any other sharpteeth from their way, for no more reasons, right?
Also, we still don't know, if they chase our gang more because of some conflict with Chomper and Ruby than chasing for getting food...