Objectively speaking, you are quite right. He is an entitled brat. If I encountered a real-life Ferris Bueller, I'm sure I'd loathe him.

But... This is a hugely entertaining film; a landmark of my childhood/teenage years, and I've always had a huge crush on Mia Sara. Plus Cameron's character arc gives this just enough dramatic weight to make it difficult to dismiss offhand (re: his monstrous parents, cleverly never seen).