What harm does science do to mankind?

I don't think so. The amount of lives science has saved:

Most operational procedures use science that was discovered by scientists.

Helicopters that airlift people were developed by engineering founded on science.

I'm sure you can think of many more.

Sure, when we have to discover things we sometimes have to do some harm in the process, but then if we didn't, we wouldn't have Mythbusters!