Bitcoin was not designed for online shopping like, for example, Paypal, bitcoin is slow and has no consumer protection, if you want to be scammed by strangers over the Internet you should shop with bitcoin.
Paypal was designed for ecommerce, it has buyer and seller protection, it's fast, and very easy to use.
Bitcoin can actually be used for online shopping. Bitcoin was at first, thought to be useful for online transactions due to its difficulty to reverse after the transaction has been confirmed for a number of times. Digital goods and credits can be quite hard to purchase with PayPal since merchants are reluctant to accept Paypal as a payment option as it would result in chargebacks. Not to mention the fees are quite steep.
Bitcoin can arguably become Paypal if there can be an escrow service which can allow 2-of-3 multisig where the seller and buyer each hold one and the escrow holds one of the keys too.
The thefts occurs mostly due to the user trusting the exchange/service too much and holds all their money in the exchanges/services. The thefts could easily be prevented if the user practice proper security measures and use their own desktop wallet for storage of their own BTC.