Then you don't understand the alignment rules at all. A person who commits Evil act after Evil act and no Good acts at all is Evil. Not "Neutral with Evil tendencies," there is no such thing as "tendencies" in the alignment rules. In order to be Neutral you need to either a.) commit no Good or Evil acts at all, or b.) commit a more-or-less equal number of Good and Evil acts. Not c.) commit a boatload of Evil acts without guilt or regret and no Good acts except those he is bullied into.
A partial list of Evil acts Belkar has performed or attempted to perform:
• Harvesting someone's kidneys who was no threat and had a Good alignment.
• Selling an attractive young woman into slavery
• Slitting the throats of helpless people
• Trying to kill an ally strictly to level up
• Killing three barbarians when he only needed to defeat (not kill) one of them
• Professing a desire to go back and kill his family and childhood friends in their sleep
• Throwing daggers at Roy just for fun
Plus countless acts of psychological abuse to his teammates for no reason other than his own amusement. And that doesn't count the 3 or 4 Evil acts from "On the Origin of PCs" that I don't want to list here.
Why on earth do people waste their time with this? I feel now like I could have Belkar turn to the camera and say, "Hey folks, FYI, I'm Chaotic Evil," and then kill and eat a fluffy puppy, and you'd still come here and say, "Well, I think he's Neutral Good."
Get over it, Belkar is Evil.