You are right in that sense no one can harm your bitcoins as they are saved in our wallets in pure form, but if some one do not know about to secure his/her wallet then the chances are there to hack by someone, so the security and safety of bitcoin is also important.
True, you have a point bitcoin can be easily stored in our wallets and the risk of lossing it is lesser compared to cash but both of these things have ways on how to secure it because money is valuable for us. Both had also risk on lossing on bitcoin it can possibly be hacked or forgotten wallet password.