Tim Suttle offers a possible explanation for why people are so easily offended on his Paperback Theology blog. It would probably be more accurate to point out that he is endorsing the explanation of another person in his post "Why Do We Become So Easily Offended?" In either case the rationale provided has some limited use. It is a partial explanation that may work in some instances.
Chocking it up to issues with an individual's "ego" may have some merit but is by no means universally applicable and is far from an adequate approach. "Ego" is such a subjective and unsubstantiated construct that it has very limited explanatory qualities. It also borders on Freudian psycho-babble. The piece is too short to determine whether Suttle is using the term in the way Freud intend or if he is trying to use a more modern interpretation.
Personally, I think it has as much to do with insecurity and fear. At least some theists probably realize to some extent that their views are not well founded. Many cannot stand even the slightest critiques of their religious beliefs for fear of where any real examination might lead. Though, I would also point out that insecurity and fear are also not complete explanations. The question, like so many, is far to complex to adhere to a single explanation.