Much more prone to theft because it is online.

And many coins are aggregated into one place (e.g. centralized exchanges) where the economy-of-scale for stealing is higher.

My 2 BTC were stolen when (using localbitcoins) I couldn't find a buyer to deposit to my USA bank account and I was in a rush. So I sold to someone who paid me in paypal. He had stolen access to someone's paypal account and so the payment was reversed.

And the point is that coins circulate, so eventually they could be stolen multiple times.    

This is not a moral and upstanding system.

We could potentially fix this with more technology (e.g. decentralized exchanges) and better education (do not use irreversible payment, offline decentralized wallets as standard, etc).

Or using a whitelisting system such as described by practicaldreamer (but then it is no longer decentralized and it becomes owned by the establishment).