I think this could be an explaination for
alttp...
The zolas in
alttp aren't zoras but a mutated species that were turned evil by agnaham (i know that is spelle wrong) just like the gaurds.
But for other games where they are evil, i think it depends on the timeline theory you are looking at. I will use one that says that
LoZ and
LA are the last two games.
In
LoZ, the zolas have been turned savage in order to survive.
It just a theory, I'm sorry if this thread somehow changes to timeline theory, but please post your thoughts...