Almost none. PIN/passwords render fraud to negligible amounts. That's why debit card transaction have fees for ~$0.10 under Durbin. Companies like Stripe make a killing whenever their customers use debit cards instead of credit cards because they're charging 2.9 +0.30 with a cost of 0.10.

But if you had to rely on debit cards only, then commerce at least in the US would grind to a halt. I believe the average American CC debt is ~$8000.