The first, and most common reason some people don't like PayPal is that they force you to provide more personal bank account/credit card access than many people are comfortable providing. Additionally, if a person passes a threshold of money coming into their account, PayPal starts charging them fees -- I think it's currently 3%.

Another issue is more political; PayPal's acceptable use policy has fairly strict rules governing use of PayPal to purchase Firearms, Weapons, and Knives. They claim the right to prohibit payments for firearms unless they specifically authorize the purchase, as well as for items that they define as weapons and certain types of knives (such as automatics), even if buying them is legal in your area or if you, individually, are licensed to own those items. It's effectively like your bank or credit card issuer telling you what you are or aren't allowed to buy.

I see others have responded while I was composing and attempting to recover from a dropped Internet connection -- gotta love AT&T.