Cedric seems like the kind of guy who sits around late at night with a cup of something highly alcoholic in his hand, ranting about the Good Olde Days. He must be an okay person at heart, since he inspires such loyalty in Gurth and the rest of his people. Wamba is willing to die for him, for Pete's sake. Honestly, though, from what we see of him, he's kind of a jerk. What kind of a guy disowns his own son – especially a son as cool as Ivanhoe?
Cedric is a Saxon landowner (what the Normans call a franklin), so he actually has quite a lot of power. He has a nice hall, lands, and servants. Yet he has a huge chip on his shoulder because he thinks he should have more power. He believes he would have more power if the Normans were not such bullies, bossing around the Saxons and taxing them unfairly. And of course, Cedric has a legitimate gripe: many of the Normans did look down on Saxons as inferior beings.
However, Cedric also has a huge blind spot about what it means to be Saxon. He wants the Saxons to hold onto their hatred of the Normans for eternity. He despises everything about them, from the style of their cloaks to their refined manners at the dinner table, to their language itself. He hates the Normans so much that he can't see individual differences between them. To Cedric, Brian de Bois-Guilbert and King Richard I might as well be the same guy.
Cedric's strong pro-Saxon patriotism leads him to make prejudiced assumptions about every Norman. And his unthinking hatred robs him of his son, at least for a time. When Ivanhoe decides to join King Richard I on his Holy Wars in the Middle East, Cedric assumes that Ivanhoe is turning his back on his Saxon heritage. But why should loyalty to a Norman king mean you can't be a Saxon anymore?
Cedric's views on what it means to be Saxon are really extreme. As Ivanhoe goes on, he starts to concede some of his more out-there assumptions about the Normans as a group. The fact that King Richard I helps lead the English outlaws against evil Normans De Bracy, Bois-Guilbert, and Front-de-Boeuf at Torquilstone helps a lot. Once Cedric realizes King Richard's identity – Norman king but good guy – he stops freaking out quite so much about Ivanhoe's loyalty to the man.
Cedric represents an older generation of Saxons. His father and grandfather fought against the Normans. He may not remember what England was like before the Norman invasion in 1066 personally (since he must have been born in the 1130s), but he does recall the emotional damage the Norman domination caused his family and friends. Those memories are less immediate and fresh for Ivanhoe, since he is younger. It's really no surprise that Cedric has a harder time thinking of the Normans as good people than Ivanhoe does; he has a stronger personal memory of the initial horrors of the Norman conquest.