The difference is a credit card is using the issuer's money; a debit card is using your money. You get no float and no "points" with a debit card. You can get an ATM card for just cash access. Debit cards are just dumb IMO.
Some are dumber than others. But if the issuing institution is decent, chances are their fraud prevention will be as well; and some of them do issue "points" or cash back.
PayPal gives 1 percent back on their business debit card. I used to make quite a bit of money on purchases with it years ago. If they ever get around to issuing chip cards, I will start using it more often again. As it stands now, I don't use it very often simply because I've soured on magstripe cards after having several of my cards compromised at a local supermarket years ago. It's the magstripe I object to more so than the fact that the card is a debit card.
I may be being a bit unfair to PayPal because their fraud protection, in my experience, is exemplary.
On one occasion I extended a trip to California for which I'd paid for the airfare on their debit card, and then made an ATM withdrawal in California after I was supposed to be back in New York as far as PayPal knew. They gave me the money, but immediately called me on my cell ("immediately" as in while I was still standing at the ATM) to make sure that I was the one who had made the withdrawal. It was a bit creepy, but impressive nonetheless.
On the second occasion, someone had cloned my card following the FoodTown fiasco and made two consecutive purchases at a Target store in Queens. I got the alerts and called the PayPal fraud number printed on the card. They immediately credited the money back to my account. They also canceled the card in an interesting way: They gave me the option of making one more cash withdrawal on the "old" card at a local ATM of my choice, while canceling it for all other uses, just in case I needed cash.
PayPal also offered to wire money to any of my connected checking accounts if I needed funds transferred more quickly than the EFT system allowed for back then. Nowadays it's next-day (and will be same-day this week), but back then three days was more common. PayPal offered to wire the money, which would be available almost immediately, on their dime, if I didn't want to wait the three days -- even though EFT from the account was unaffected by the card compromise.
So really, I probably shouldn't be so concerned about PayPal's debit card fraud resolution. The one time it happened there was literally nothing else they could have done to make it less painful other than flying someone to my front lawn in a helicopter with the replacement debit card in hand on the same day. Granted, my PayPal account gets a lot more activity than most because they're also my credit card processor, but I doubt that I was treated any differently than anyone else would have been.
The other time a debit card of mine was compromised was a result of the same supermarket breach. On that occasion, my credit union decided that a particular jewelry purchase from an online vendor in Thailand someone was trying to make on my card was probably fraudulent; so they declined the charge and called me at about 5:00 a.m. to check it out. When I confirmed that it was fraud, they canceled both my business and personal debit cards and had new ones waiting for me at the branch when it opened that day. When I got there they told me that had the charge gone through, they would have immediately refunded the money to me.
The credit union has since switched to chip cards, and I still use them from time to time. USAA's debit cards are also chip-enabled and have been for quite some time, and I use theirs with no hesitation if I prefer not to use a credit card for some reason. It's the magstripe cards I don't use anymore. Chip cards aren't perfect, but they're a heck of a lot better than magstripe.
As to why not use a credit card rather than a debit card for all transactions, that's just a habit held over from the days when my credit lines were skimpier than they are now. I didn't want to use up my credit lines with a bunch of routine, recurring purchases like gas, groceries, and utilities. Nowadays the credit lines aren't an issue; and because the credit card issuers have started granted more generous rewards on those sorts of purchases, I've started switching over to using credit cards for more of those purchases.
Rich