It does benefit mankind. For example, if our organs failed, we
can create a clone of us and transplant it to our body. No need to
worry about rejection from the body.
However, what do we do with our clones? Do we just clone them to
get the organs that failed us? Religious people don't agree with
it, so do the non-religious people.
Besides, too many people on Earth is not good. It will deplete our
natural resources even faster. That's why we don't we want
it.
The third reason is that despite having the same DNA as ourselves,
the clones have their own thinking. Your parents can't teach them
the same way they taught you. Even if they do, they still have
different thinking from you. Would you like your own clone to be a
cannibal? Your clone feels that it is right, but you feel that it
is wrong. How about the police coming to your house to arrest you
for a crime that your clone did? Same DNA will result in same
thumbprint.
Cloning also has side effects. Dolly the sheep died younger than
original sheep. As cloning produces the same species with the same
weaknesses, if a disease strikes, it will wipe out the whole
species and that species will become another dinosaur. That's the
reason why nature blessed us with evolution. With evolution, it
will prevent the total wiping out of any species unless some
disaster strikes (asteriod hits the Earth or another Ice Age)
