Your case wasn't a security issue though, right?! Also, I might be wrong but I don't think that PayPal's offering is of a platform that makes it easier for you to cancel transactions.
You're right! I was being careless and stupid. I was just surprised how easy it was to miss the recurring charges agreement. That experience made me wonder what value PayPal actually offers to buyers (I don't know much about the sellers' side). If people are worried about fraud, their credit card provides more protection that PayPal.
Once I paid $5 to buy the trial version of some software tool. Since I didn't know the seller, I used PayPal thinking it would offer more protection. After one week I was charged another $100 for the full license. I contacted the seller asking for a refund, but they declined it on the grounds of me having already accepted "recurring charges" on my PayPal transaction. Apparently I had but it was kind of hidden on the transaction and I hadn't paid enough attention. I contacted PayPal but they refused to help either. Finally I reached the credit card service attached to my PayPal to initiate a charge back. But at the same time I informed the seller about my intent and they refunded me instantly.
So long story short; don't use PayPal and if you have to, use only reputable credit cards. Never use your debit card on PayPal. PayPal doesn't protect you any more than your credit card does.